Transcript for:
Meiosis Overview and Key Concepts

problem meiosis my mitosis can occur in other body cells but meiosis occurs only in the reproductive cells where did you come from actually meiosis was the basis of you living without meiosis you didn't have existed so let's look at meiosis in detail so it's a type of cell division that results in four water cells each with half number of chromosomes to that of the parent so it means that meiosis starts with the uh it starts with the one cell this cell divides and then you form four Dora cells these cells they have half the chromosome number to that of a parent if you have started with the four chromosomes it means that uh the these cells will result in two chromosomes that's why you're saying that half the chromosome number of that of the parent if the main the body cell is having 46 chromosomes then the the reproductive cells or the daughter cells which are resulting from that are going to be having between three and then from the mother also 46 they are going to result into 2.3 so the process of reducing these cells into uh have the chromosome number that process or that reproductive process is what you call meiosis so what does meiosis result in so this message will result in the production of gametes gametes these are the sperms and the over and talk when you're talking about the humans and then plants you're talking about spores in the pollen grains you can talk about the obvious those are some of the things uh which as a result of of meiosis so in humans or in animals it occurs in the ovary see this colored word in the ovary and then these ovary they produce what you call the over so the reproductive cells in the film in the females call them over if this one is called the other if there are many you call them over and then uh in in male in male because it is occurring in testis and then in this uh what we call we call them spermatozoa the cells which are being produced we call them spermatozoa so in female we call them ovary those are the over raised ovaries produced over and then in in testis uh they produce what's called a spermatoso what about in plants in Plants occurs in the ovary still but what it produces over reproduce What's called the obvious meiosis occurs in the anthers and then what it is being produced is what you call the uh the Polynesian so the question can come and say that um other than the ovary in animals which other place does uh meiosis occur that is testis and what does it produce it produces what we call this spermatozoa and then in in in in Plants uh it occurs in the ovary it produces what you call the obvious basically uh that's what you need to know about this first introduction of of meiosis you know myself is basically the cell divides and the the most important thing to divide is the nucleus so so we need to know the nucleus to do a recall about the nucleus because we saw the nucleus at the beginning of DNA and also saw the nucleus in the grade 10. so let's look at the nucleus the centrosome and then the cytoplasm nucleus contain the genetic material what about cytominees uh cell and then plus means a fluid the fluid of the cell so basically this is what you are going to look at let's look at them in detail so this is a cell it has a nucleus outside you have what's called a cytoplasm then in the cytoplasm you have what called the centrosome centrosome why do we talk about the nuclear centrosome and discipline because uh uh this uh the DNA you'll find it there and then it is the central zone which which produces the centrioles and the centrioles spindle fibers which hold the chromosomes in position that's why I talk about it and then there is a time when this one disappears and then you remain the content of the cytoplasm so the nucleus disappear and then remain only with the content of the cytoplasm so basically that is a nucleus and then when it brings it in exam it looks like this so this is a nucleus as a nucleus but the nucleus has a density body which we call the nucleolus nucleolus then outside the nucleus if you have the nuclear membrane which has the extensions extension which you call the endoplasmic reticulum but because it has the ribosome they look rough then we call them the rough endoplasmic reticulum the rough endoplasmic reticulum so basically uh that's it it has the nuclear power the holes where substances go through most especially messenger RNA in this case and other substances then it has what you call the nucleoplasm the nuclear the plasma of the nucleus meaning that the fluid of the nucleus the nuclear envelope uh that's what you call the nuclear membrane then the ribosome we say that the ribosome that sites for protein synthesis chromatin this one is one which condenses to form chromosomes and then you have the nucleolus then you have the rough endoplasmic to come so we have explained all that so when you look at the nucleus or when you look at the DNA basically that's what you see you have when the chromatin Network condensed you from what you call the chromosome so the chromosomes uh they condense you see they have condensed and then after that you form the real structure of a chromosome it looks like this so that's the structure of a chromosome now let's look at the chromosome in detail so we have seen where the chromosome come from it cannot exist without DNA with this specific genes you see it has specific genes so let's look at the structure of a chromosome why do we need to look at chromosome will you resemble your father because of the chromosome because of the genes you obtained from your parents your father your mother what about those who don't resemble the father and the mother but they resemble their grannies we shall see another question what about why so in this topic we're gonna see why why do you resemble uh your neighbor why do you resemble when you go somewhere when you go somewhere someone can say that when you resemble someone why do you resemble someone those are some of the questions we are going to answer and this is the reason why we need the structure of the chromosome so the structure of the chromosome chromosomes are thread-like structures present in the nucleus the thread-like their thread-like it means that they are like strings certain like structures found in the nucleus that's why we talked about the nucleus which carry genetic material that's why you resemble your father that's why you resemble your mother which carry genetic material from one generation to the Next Generation so it means that your kids will try to resemble you yes then you're saying that each chromosome is made up of the DNA we saw this that DNA genes are almost the same thing but on a different scale so this DNA or these genes are tightly coiled many times around a protein called histones so the Houstons we saw this when we were talking about uh when you're talking about protein synthesis and also the when you're talking about the structure of the DNA yes so the the coil around to format called the histones that supports the structure of the DNA because the genes cannot just exist there in in in in in air they they need to have a support so the support which the support we call it them histones so these are the support which make the DNA strand to stand or to be where it is and so that the chromosome can be formed when this DNA condense all right this is the structure of of of chromosome before remember we talked about during DNA replication that when does it occur we say that it occurs before the cell divides or before meiosis so before the cell divide the chromosome will look like this yes they will look like this therefore we call this one single stranded chromosome chromosome one chromosome sometimes we call them unreplicated chromosomes they have not yet done DNA replication but the moment DNA replication occurs this chromosome is going to change from this format to this format that's why we say that it doubles the chromosome number don't say that it increases the chromosome number it increases the chromosome number it increases the genetic material from what to what the best answer is to is double the chromosome number doubles the chromosome number so that when it was like this then it becomes like that so uh this is the centromere the center of the chromosome we call it centromere the two chromosomes which look alike it means that uh they share the same structure yes and the position of the genes on them then we call them homologous chromosomes homologous chromosomes so one chromatid from one chromosome and another chromatid from another chromosome because they are homologous chromosomes therefore because we are talking about chromatids of homologous chromosomes then they are going to become homologous chromatids why because we say that they are coming from homologous chromosomes but each part is a chromatid therefore they become homologous chromatids so um so sometimes as I say that this is called unreplicated chromosomes and then we call these ones they're replicated the chromosomes or what you call homologous chromosomes so each of these have has two names and they replicated chromosomes or single standardic chromosomes and then these ones double Stranded the chromosomes are replicated chromosomes so the number of chromosomes in each cell is a characteristic of organisms for example humans we have 46 chromosomes you'll find out that drosophil Amino investor has eight chromosomes you'll find out that the ship has over 60 chromosomes so each organism has a specific number of chromosomes it has and you might find out that the biggest organism has fewer number of chromosomes so that's how life or how that's how God is uh so it doesn't matter whether you are big or smaller but you might have your own uniquiness that we are saying that chromosomes which are single thread become double when the chromatid joined by Central mayor so the center of the chromosome we call it centromere as a result of DNA replication so if DNA replication occurs as we said now the single stranded chromosome are going to become double-stranded so that's why you call it unreplicated chromosome or single strategic chromosome the moment DNA replication occurs it becomes double-stranded chromosome or replicated chromosomes yeah so what are some of the difference between uh the haploid and diploid higher die means to employee means you are describing your body yeah so help me half means this is derived from the word half half the chromosome number if a human being is supposed to have 46 chromosomes so when you are haploid or with the structures haploid because they have the chromosome number of that organism for example if organism has 20 they haploidy state of it is going to be 10. if the organism is having uh 32 the haploid number of that uh organism or haploid state of that organism is going to be 16. so haploid means half the chromosome number deployed means doubling doubling what does mean where is the double there it means that half from the father half from the mother and then they double it when they double then they format because they diploid or deployed the way you uh pronounce it so haploid is the quantity of the cell or organism having a single set of chromosomes they have what's called a single set of chromosomes so if you have chromosome number from one to two from chromosome number from one to ten these chromosome numbers these chromosomes must be in pairs so if you are haploid chromosome number one to ten they'll be in single single single there will be one one one one they want to be in pairs so that's what you call it haploid but if it is deployed is when the cell or organism has a pair ID or two set of chromosomes paired or two sets of chromosomes one from each parent it means that one from the father one from the mother when they combine because there are two organisms contributing this then you form the word die which is um two and then employee means a body yes it's a state which you describes organism with the two sets of chromosome systems one from the father and one from the mother that's the meaning so for sexual reproduction to take place sexuality means that it must include the gametes it must include the gametes and must include sex reproduction to take place yes what happens uh a haploidy metal damage that is if we are talking about humans we're talking about sperms will fuse with the haploid that means that it will refuse what is a haploid metal gamete half of the chromosome number from the male they got me to have half of the chromosome number from the male if the male is 46 the gamete is going to have or the sperm is going to have 23 chromosomes we refuse with the haploid number from haploid from the female also now the female is going to produce 23 when they fuse together you form fertilization so when they fuse together that process is called fertilization now you form what you call a diploid because half from the father half from the mother then because it's half half from different people then it becomes die becomes two they fuse together and then um when you're talking about fission overallization we are not talking about sex because there is the vision of fertilization can take place without sex meaning that how many maybe they used a male just give out the sperms so when you're talking about fertilization we're talking about sex has already occurred and then the sperms they swim along the female reproductive system and then Fusion will take place this Vision can even take place someone had sex at night and then you're walking on the street Fusion is taking place imagine what did you know when when was your fertilization took place you don't know if any opinion doesn't know okay those are the wonders of the science all right if you need more questions concerning about this reproduction go and visit our YouTube channel which you call Bright Doctor Bright doctor I'll give you the link in the description below so that you can understand it better all right the result is a diploid zygon the result is a deployed zygote so when you have the haploid haploid you form a diploid or a diploid zygote so it means that when the sperm fuses with the oven you form what you call a zygote but this zygote has a deployed number of chromosomes this body has a deployed number of chromosomes it means half from the father half from the mother all right haploid half which is indicated haploid is indicated as one end and then diploid is also indicated as one sorry haploid from the mother one end for example haploid from the father for example is also one end so when you combine them you form the diploid which is whole yes is is the hall now half and half you get hot yes basically half from the father half from the mother from the diploid die Minister meaning that contribution from one person another contribution from another person so because they this resultant uh body is having two contributions then we call it a diploid so it is indicated as to n we shall be using this language so you have to know when someone uses this language you must know what it means so is zygote is where a fetus develops from we shall see in the videos we're gonna be releasing soon uh uh how is the zygote form you see the sperm of swimming after after sexual after sexual intercourse you see this sperm swimming going to the Overman fertilization takes place for more detailed about this visit what you call the bright Doctor Bright doctor uh just a link below drop your question then we shall give you the answers on that YouTube channel but for purpose of passing exams we don't go far away from this but there we can describe as much detailed as you want so uh sexual sales is I.E that is palms and other are haploid so we call them haploid they're one end 23 chromosomes in humans so it means that the other organisms have different chromosomes so we have what we call the somatic cells so it means that you have two types of cells we have what called the six cells those are the gametes I say that meiosis can only take place in these cells we don't find meiosis in any other cells only in the gametes so you have the other body cells some some some some comes from the word summer which means a body yes so these are body cells are diploid which means that they're 2N if they are 46 it means that the haploid is going to be 23. but the question when it comes it does not bring only human you can only talk about 46 if they have specified in the question that this is a human cell because they can bring yourself with the 10 chromosomes they can bring yourself with four chromosomes if they don't specify that this is the human please don't use 46 because the question is not asking about humans there you have the 23 pair of chromosomes that result in the zygote are divided as follow how number 22 pairs these are the number of chromosomes we have in the body 22 pairs that is from pair number one to pair number 22 we call them autosomes autosomes it remains that how many chromosomes we have 44 because this is a pair pair number one appear number 22 we call these ones Horizons one pair of six chromosomes that are one pair that is the 20 30 pair we call it six chromosome or scientifically we call them gonosomes scientifically we call it gonosomes so this pair is divided into two we have what's called The xx which is female and then we have X Y which is male so it means that um females always they will have XX and males will always have X Y ah there is a questions which is supposed to be posed here why if if if if females are XX and the males are X Y it means that it's the mayor's to determine the sex because female have X also male has eggs but female don't have y but male have y so it's the male two males to determine the sex of the human being the sex of an individual so males you must stop you must stop saying that ladies are only giving you females they're only giving you boys they're only giving you girls say I'm giving myself boys I'm giving myself girls it's you who is determining this however there are some other factors which also determine it can be on the side of the female for more details visit the bride doctor drop your question there we will be able to answer those questions if you drop the question there then I'll be able to answer those questions and humans have what we call the chromosomes from we say that from chromosome number one to chromosome number 22. these chromosomes are arranged in a specific order and they appear in a specific way they they are in pairs and then they describe different characteristics in the organism so let's look at the karyotype the the composition of the nucleus which kind of nucleus which kind of nucleus do you have the chromosomes the type cardio is is is derived from the nucleus and the type so with type of the nucleus do humans have thus derive the name of Cario type humans sell America foreign have 46 chromosomes and then this is 46 chromosome are arranged in pair these chromosomes are arranged in pairs it means that they can only exist as singers what does it mean if you're not married all right it means that they are arranged in pairs each pair is different from each other oh each pair is different from either by so this these these pairs are different by how do they differ how do they differ they differ by shape size and genetic composition so pair number one is totally different from Pair number two by size shape and the genetic composition it means that what pair number one determines is not the same thing what pair number two determines for example you'll find out that chromosome number 23 pair number 23 will determine the sex you cannot find this in other chromosomes so they vary in shape size and the genetic composition from Pair number one to pair number 22 number one to twenty two are called autosomes what about 20 30 pair is called gonosomes which has x x for female and the X Y for male X you have to know this x is longer and bigger over y why X is longer and bigger over y question why why is X longer and bigger but right doctor will answer that but on the purpose of this um X carries more genes compared to why compared to y so so so uh a career you type an example looks like this you see that chromosome number pair number one number two number three number four the the they vary in appearance shape and also they vary in the genetic composition so from 1 up to 22 we call them all this we call them gonosomes we call them aerosomes and then the 22nd pair we call it Gunners so basically uh does it uh the vision of the process of mitosis it's not it's advisable before you start meiosis to do a revision concerning about concerning about the process of mitosis so guys our next video as we say that we're gonna be having uh prices airtime uh uh meals yes we send you a vulture and then you buy whatever you want to buy it can be a school bag t-shirts we have a lot of gifts to give out on our YouTube channel so please don't forget to subscribe don't forget to subscribe like share so that others also benefit from this content and then we're gonna be having all the subjects so we are trying to increase this so mitosis occurs in every living organisms in the somatic cell to produce those are the body cells other cells other than sperm and ovum to produce genetically identical cells so you can have a hole on the mouse on on the cheek and then uh you need meat so what they can do they can cut the bum and then they put on the mouse and you move with the bum or or or on your face basically why why do they do they do that because these cells they undergo what's called mitosis they are genetically identical they are genetically identical they meet from your bums is exactly the same as the meat from your face in terms of the genetic composition so two identical cells are reproduced two identical cells are produced with a identical chromosome number equal to the original cell it means that the parent and the babies or the daughter cells they're exactly the same there is no difference that's why when you get your wound another meat develops those cells which develop the exactly the same mitosis has only one cell cycle I it doesn't have that that mitosis one animal it only has one cell cycle only one silver cycle it means that meiosis when on on the side of meiosis it has two cell cycles meaning that it has meiosis one and also has meiosis two so guys let's look at the process of meiosis yeah the process of meiosis was a very good introduction of of meiosis now let's look at meiosis in detail and this will be our next topic tomorrow don't miss it don't forget to subscribe like and then share the video we will be having gifts uh prizes in the our next videos starting from meiosis thank you very much and also don't forget to like subscribe and share our new YouTube channel in the link below called the bright doctor inside was giving me the lesson thank you [Music] [Music] [Music] please use the link below to get the notes questions and other videos don't forget to subscribe like and share to others for our daily new videos yeah welcome back guys welcome back we are today we are going to be looking at what you call the process of meiosis so we saw the introduction of meiosis and today we'll be looking at the detailed process of meiosis and where are most questions come from in examination yeah don't forget that we say that in this video we'll be having some some gifts some gifts for those people who are watching the process of masks don't forget that we said that meiosis is a process whereby one cell divide to form four the other cells these cells are genetically different from each other and from the parent the process of meiosis we say that a type of cell division that results in four dollar cells each cell with half the chromosome number two the parent so message is a continuous process it's a continuous process but it's divided into different phases uh and and and events so the events um for example the first event is what you call the interface interface is a is not part of meiosis you um you must know that interface is not part of meiosis it's just a growth phase because meiosis is regarded as a reproductive uh process in the uh reproductive cells which are determining the the cells which you call the gametes so um it includes a DNA replication that's where where DNA replication takes place remember when you're talking about DNA we asked a question where does it occur we said in the nucleus when does it occur occurs before the cell divides or it occurs during interface So when you say before the cell divides it means that uh interface is not regarded as a phase of meiosis it's just a growth phase it's like saying that uh you give us a baby and then a baby immediately cannot give birth to another baby need some time for this baby to grow so that now uh once the baby grows then is ready to reproduce when the cell divided and then goes to the last phase it does not divide immediately no it requires some time for it to grow so during that process of growth is what we call interface and the things which occur in that phase some of them is DNA replication doubling of the uh DNA chromosomes which are single-stranded they become double we saw it that we have what we call the unreplicated chromosomes when they double they become the replicated chromosomes so when the the chromosome has one state then we call it uh an unreplicated chromosome or what you call single standard chromosome but when it becomes a double as we said as you see it here it becomes what it it is called uh replicated chromosomes or double stranded chromosome so each chromosome will consist of two chromatids joined together by a centromere so a chromosome it must have a chromatid it must have a centromere joining it if it is replicated the chromosome it will have two chromatids and these chromatids must be joined together by a central ner centromere is the middle part of the chromosome then um DNA replication what happens in DNA replication DNA replication helps to double the genetic material to double the chromosome number as I said that we don't set increase the chromosome number as we ask a question it increases the chromosome number from what to what so we need to say that it doubles the chromosome number of genetic material so the material so that um genetic material so that it can be shared equally by the new cells arising from the cell division it means that now these cells the new cells which are going to be formed they're going to have the content they're going to have the content they're going to have the chromosomes they're going to have other cell organelles equally shared equally because each cell must have this content so if it doesn't have then it means that it will be empty and then you won't be able to survive so it is the function of interface the growth phase to bring about the doubling of these organelles and the doubling of the genetic material so that each cell each cell has a equal amount of the genetic material and also the cell organelles if we have said that our interface is not the part of meiosis then what are the phases of meiosis number one we have what called the prophase number two we have what we call the metaphase number three what called the anaphase number four we have what the telophase and then we go to prophase to prophase metaphase two anaphase two Terra phase two so we are talking about uh prophase metaphase anaphase what is it what does it mean prophase means preparation Pro means preparation P versus P then you have metaphase versus middle m versus m and then anaphase versus apart a versus a and then t means still phase T versus D so even in prophase two the metaphase two anaphase two and then there are phase two so we form a if you take the first layer we form what called ipmat This is in different color it means that this in interface is not part of meiosis that's why we don't have interface one and interface two we only have interface so it means that it's not a part of meiosis so the the the the process of meiosis begin with prophase metaphase anaphase and theraphies whereby we say that this is a preparation middle apart and then they have reached the what's the terminal what are those things which we are talking a middle apart terminal what are they we are talking about with the chromosome as you see them here so this is trying to show you exactly uh what is happening so it means that you start with one cell the one cell divide from two cells and then these two cells divide from four cells but actually what is really happening for this cell to divide is what you're going to look at in the details of each phase let's look at meiosis one meiosis is divided into two phases into two divisions not phases the first military division and the second magnetic division so in the first metric division it will have prophase one metaphase one another phase one two phase one and then the second metric division we will have uh profits to metaphase to anaphase two and then third phase two so the market the first meiosis uh this is called a reduction division whereby when we talk about reduction division you start with 46 chromosome at the end of mass is one you end up with the 23 chromosomes 23 chromosome in itself hence we call it a reduction division this division results in the reduction of the number of chromosomes from 46 um to 23 in each cell so uh the resultant gametes are haploid it means that they have one set of chromosomes from chromosome number one to chromosome number 23 they are not paired it means that they are single haploid half that means that the cell has 23 chromosomes you know it's 23 pairs of chromosome all right let's look at the phases of of of meiosis the first phase is prophase which means preparation the cell is preparing for whatever is going to be uh doing so the first thing is chromatin Network we say that chromatin Network means that uh uh entangled entangled DNA DNA is in form we don't have a direction when we look at it we don't know where it starts or we don't know where it ends so it is chromatin Network when it condenses it forms it becomes thick when it becomes thick it forms what's called a chromosome so the chromatic Network contains when they condense it means that now that it has formed the chromosome now these chromosomes the chromosome which look alike homo which means the same logos which means structure so it means that chromosomes which look alike chromosomes which look alike they are going to come together that's why you're saying that homologous chromosomes are formed it means that the chromosomes should look alike they come together when these homologous chromosomes the way you see it here when they they they they they they they they come together they cross over what do they use to cross they cross using the chromatids the one chromatid of one homologous chromosome crosses with another chromatism of another chromologous chromosome and then the process continue so the spindles already starts to form it means that now the spindle fiber they start to form and then once they start from the nuclear membrane starts to disappear let's look at the diagram here so you see that here um the the the the the chromosome they condense the homologous chromosome we see this one is short this one is long so this shot cannot go with the long one no the shot goes as well the shot the long one good is the the long one that's the principle this these chromosomes they come together and then the chromatids they cross each other when they cross each other we call it crossing over that's why we're saying that crossing over takes place and then the point where they cross over we call it chasma we're going to look at this in detail and then now this window they start uh the same rules they start to move to opposite poles as they move yes as they move they spindle starts to form so once you see something like this they have crossed like this then you just know that yes this is is profits why because the chromosomes are crossing over homologous chromosomes are crossing over we don't have crossing over anywhere else except in prophase one no even not in prophase two we only have it in Phase One why in Pro phase one because the chromosomes are still in homologous pairs let's look at the process of crossing over so we have seen that the homologous chromosome the chromosomes which look alike they align together when they line together one chromaterial of each chromosome overlap so it means that they cross each other when they overlap these chromatids they must be overlapped based on the homologous pattern for example it means that the one chromatid form one homologous chromosome and another chromatid form another homologous chromosome they cross over and then when they overlap and they cross over it means that they cross over at a point called chasma and then crossover takes place at a point called chasma if it is one with chasma if there are many we call them just matter so when we say chasma or chiasma burning on the kind of English you are using then um chasma or chasma is is is is is one is a point where these two homologous chromatids cross over during prophase one and then now the chromosomes separate so it means that now they have formed the different chromosomes I always ask this question to to different people are you sure your father is your father why am I asking you that you don't resemble him actually you don't even resemble your mother you walk you go somewhere and then you find out that you resemble someone why and they ask you that hey when are you resemble someone I I know that why basically he might be your father but because of crossing over this made to the exchange of the genetic material if you came from the same father same mother you breastfeed on the same breast of your mother why don't you look alike it means that this crossing over this process of meiosis helps in bringing about variation among organisms so it is a very important process to make humans individuals different from each other and then this helps in the survival if all of us we are the same then it means that we won't be able to survive imagine everyone is rich do you think that there will be someone who is working for another one everyone has money you think I would have taught you this no because I don't need you don't need this no one would have been watching you don't need this you have your money what else you want but because there is difference among these organisms among us then it brings about what called competition hence different people will work differently and in different environmental conditions so that's the purpose of meiosis to bring about variation among organisms of the same species all right let's look at continuing with the process of crossing over so these differences is being brought about by crossing over imagine a father producing uh over 100 million sperm for a single age actuation and then this sperm each sperm is different from each other what made them to be different from each other is the process of crossing over because it forms different combination of chromosomes all right let's look at so we think that you have one homologous chromosome and another homologous chromosome they come together yes when they come together they overlap the chroma homologous chromatic overlap at a point called chasma yes if you look at ABC and then inside ABC yes when they cross now this one takes this red and then the red takes the blue that's why you see it here the blue takes the red and then the red will take the what the blue this chromosomes during crossing over scientifically we call it a bivalent or bivalent based on how do you write that how do you pronounce that bivalent or be valid and then after that they separate so that each chromosome has genetically different uh each chromosome has different uh material from uh one another look if you see that ABC starting with a b c but this is a small error the small era was found on this chromosome and this is one ABC but this one is the capital letter the capital letter came from this if you look at it here it came from the blue it means that the blue they already took the blue and then the blue took the what the red so because of this it's gonna cause different uh gametes being formed and then if you look at it sometimes we can bring it in the exam like this homologous chromosomes when they cross they cross from top so when it crosses from Top it means that you have to draw it on top don't grow it down that's one of ways of of losing max if you don't show the variation correctly so you have the chromatids crossover and then the exaggerating material or the information and then now the chroma chromosomes now have new combination of the genes guys don't forget that I told you that there is a gift uh in this video just click that link below it will take you to a specific page on our website and on that page there is a code for you to obtain that airtime enjoy it when you get it when you load it on your phone let us know that you got it thank you very much let's continue and then you're saying that the second phase is metaphase one metaphase one mirror means middle it means that now the chromosomes are always in homologous pair homologous chromosomes randomly align along the Equator along the Equator of the cell in Pros it means that they they align along the Equator in two rows one um from chromosome one chromosome number one to chromosome number 23 another one is from chromosome number one to chromosome number 23 that's what it means each chromosome is attached to the spindle uh the spindle uh thread from each pole this is what I'm trying to say so they align in two rows you see this they align in pros and then these chromosomes are being held by the spindle see each chromosome is attached uh uh to the spindle threat from each other they do this they do this Arrangement randomly so the key point is homologous because they're in pair and then each other you see this one cannot come here no they must be together like this homologous chromosomes yes that's a key point and then they they come here randomly remember we have 23 pairs but we're just showing you two pairs yes they are here randomly so it means that another one can be yeah this one can be on top so this set can be on top this one can be down or this chromosome can be decide this one can be decide that's what we call randomly so when they separate we're gonna form different cells so each chromosome is attached to the spindle fiber or spinozade from each pore that's what we are trying to show you that is threads are attaching the what the chromosomes from each pole so after that once they are done with this then they start to move apart which you call anaphase so in anaphase the spindle is already shortened they try to pull when they shorten they pull it's like when you your body builder when you carry something the muscle is shortened when they shorten they pull yes so they pull uh the homologous chromosome to opposite talls and then the chromosomes what happens to the this chromosome the homologous chromosome pair then they do what they they separate the chromosome of the chromosomes of the homologous pair they separate it means that now they move to opposite poles this is what is happening so now they move to opposite poles and then now uh when they move to opposite poles now they reach the pole so in telophase each chromosome or chromosome reach at the poor of the cell and then once they reach the power of the cell the cytoplasm and the cell membrane divide when the cytoplasm and cell membrane divide that process is called cytokinesis we call it cytokinesis the vision of the cytoplasm and then the two haploid cells are formed to haploid cells are what are formally and then the nucleus the nucleus or the nucleolus that dense body in the nucleus they reform then it reforms and then lastly the new uh nuclear membrane forms and then now they cell appears to be a full cell so this is uh what I'm trying to say yeah so now you have a form of two cells now these cells cytokinesis took place and now this is the nuclear membranes that will reappear and then the cell goes back as if it is in profits so now when it reaches there now now each cell each of it it will undergo meiosis too it means that now this one is going to go under meiosis two even this one's gonna go undergo nice is true so that you form two here and two here so when you add them you form four cells so when you go to meiosis two what happens now prophase two you go to prophase two when it's meiosis two profess it becomes prophase two items they too must be there if you don't write it there we won't give you a mark because we don't know which prophase is it so prophase two what happens the nucleolus remember we said that it it appeared they reappeared so now the nucleolus and the nuclear membrane they disappear again but now here we don't have crossing over so the new uh spindle fibers are formed yes they start to form and then the chromosome become visible it means that they condense and then it becomes visible and then now once they become visible now it's ready to undergo metaphase they go to the middle of the chromosome uh the cell so now you see it yeah now it is forming like this and then now they are ready to move this this thing to attach themselves to the chromosome but now we don't have homologous chromosomes we have chromosomes which are not homologous it means that crossing over cannot take place because it already took place before before yes so now uh in a metaphase two the individual chromosome line up here individual of one chromosome aligned along the Equator singly or individually so the other side we say that chromosomes they align along the Equator in homologous pair and then randomly here they align along the Equator singly or individually so you have to know the difference so sometimes you ask you the difference in my usage one animals is two you can use the process to differentiate between the two so at the equator of the cell with the centromere attaching the spindle fiber or Central May attached to the spindle fiber and then now uh this is the picture if you rotate it you will see that these chromosomes are in the middle you see the in the middle if this is the pole and this is another pole they're in the middle so this one becomes the equator remember I say that equator is an imaginal line it's an imagined line it's a line which we just imagine but the line is only there is a marginal line which divide the cell into two equal parts the same thing equator of the earth marginal Line running from east to west and dividing the earth into two equal parts we're just imagining but the line in actual sense is not there we just imagine that that's the center of the Earth so we just imagine that's the center of the cell so in anaphase once they're in the middle they now they have to separate to opposite poles so in anaphase two you have spindle fibers start to form so the spin of fibers they contract when they contract it means that now they pull the chromosomes apart but now because they are single chromosomes they are non-homologous now is this the the the the the the chromatids which are going to separate remember chromosome is divided into two chromatids now the one chromat is gonna go one side and another chromatid is going to go to another side of the cell so this is what I'm saying that now the chromatids move to opposite it was together here now this one pulls it inside and this one pulls this side check the direction of the it's not facing this way is facing that way because the force of pulling is coming from the side so that's why it's supposed to be like that when you're drawing make sure that you are you take caution when you're drawing it so that you draw it properly and it's checked about the shadings also the shadings are very important when you are doing it the Dora chromosomes reach the poles once in in telophase 2 in telophase 2 the dollar chromosomes reach the policy when they reach the poles we don't call them chromatids anymore we call them chromosomes actually that's what we call single standard chromosomes or any replicated chromosomes so it's supposed to get time so that this time allows these chromosomes to grow so that now it becomes double-stranded again that's why we need what you call interface so new nucleus uh then forms it means that the nucleolus also come back what it means that it reforms then the cell membrane of this of each cell constrict and then the process of cytokinesis occurs when the cytoplasm divides now the process of cytokinesis occurs and then for haploid it must be haploid there are cells are formed and then now each daughter still have have they have the chromosome number to that of the parent so that's why you're saying that meiosis is the process whereby one cell divide to form uh four dollar cells which are haploid or which have half the chromosome number to that of the parent and these chromosomes are genetically different because of the crossing over which took place so the daughter cells are genetically different as I've just said and then these are the cells which will form we form four other cells and then you you see we don't call these ones chromatids we call them single surrounded chromosomes watch out to this before you write your SBA so the importance of masses what are some of the importance of meiosis let's look at the importance of meiosis so I'll start from there with the importance of of meiosis anxiety is giving me a lesson thank you very much [Music] please use the link below to get the notes questions and other videos don't forget to subscribe like and share to others for our daily new videos So today we're going to look at the importance of meiosis non-disjunction how does non-disjunction bring about Down syndrome and then we wrap up with this topic and then we can start the topic of reproduction in vertebrates so that the other time you come back we can start a reproduction in human or what you call human reproduction all right importance of meiosis before we start the importance of meiosis don't forget that meiosis is the process whereby one cell divide to form four dollar cells and each cell has half the chromosome number to the parent it means that the cells which are being formed under meiosis are different so and then we we say that meiosis results in haploidy cells and these cells are specifically for gametes based on that information we can identify some of the importance of meiosis so what are some of the importance of meiosis the first one is the production of haploid gametes we'll talk about the gametes we say that gametes these are sperms and over so these sperms are haploid which means that if they are diploid if the pedestal is deployed it has 46 chromosomes now the gametes they're going to have 23 chromosomes if it is a human cell so number two is having effect of the meiosis overcomes the doubling effect how is this having effect being brought about when you talk about having effect remember uh remember that that we we started with the uh you start with uh 46 chromosome this 46 chromosome they divide and when they divide you form uh one cell another cell and then this one also divided from another cell another cell we want to explain the effect this issue of having effect now this is 23 this is 23 this is 23 this is 23. so now it means that the sperms or over which are being formed here they're going to be uh they're going to be 23. now if you bring about um if you bring about for example a Spam fuses or fertilizes the ovum the ovum and then these are gametes remember the engineer this is 23 and also this is doing three so now when they fuse during the process of fertilization now you go back to 46. so it means that this is Fusion this is fertilization so this is the doubling effect this and this they double to form 46 but now meiosis is going to divide them now to form 23 23 so that's why here they are saying that the huffing effect this having effect this having effect is being outcomed by it by the what the doubling effect of fertilization so this is fertilization while this is meiosis so it means that this helps us to keep the the number of chromosomes in one generation to the Next Generation constantly but if this having effect was not there it means that if fertilization occurs now it would have been Now 46 46 and then you form another one which is 92 then 92 again 90 to 92 again you you form a big number so this halfing effect this um doubling effect is being out uh come by doubling effect the having effect out um overcomes the doubling effect of fertilization so meiosis results in reducing the chromosome number so we're seeing that thus maintaining the constant number of chromosomes uh from one generation to the Next Generation so now uh we are saying that um this produces number two another thing is um it produces what you call the genetic variation remember in in in any prophase one remember in prophase Pro uh phase prophase one you have a process called the crossing crossing over this crossing over it helps in in exchange of genetic materials so because there is exchange of genetic material then you will have different sperms uh we know that you produce over 300 million sperms for a per a single generation so each pump is different it's as a result of rough phases during the prophase uh in the process called crossing over so it brings about new recombinants new combination of genetic material um we are different from our sisters and brothers is because of basically uh because of the process of crossing over why is meiosis important for survival do we need uh reduce meiosis for survival or do organisms which don't under meiosis survive we need to this mouse is so that we can create differences among individuals of the same species if these organisms are known at the same then automatically it means that there won't be differences imagine I I ask you a question last time that if everyone is Rich what will happen if there is there are no differences among us if everyone is clever you don't need to read everyone has the information it means that there will be no competition so the reason why mercies is there to bring about the differences among organisms of the same species you can survive in hot environment you can survive in in cold environment you can survive and add-ons who survives in hot environment can't survive in in cold environment so it brings about that now all the the environment can be occupied by different kinds of people yes if you can't survive then it means that you have to migrate to the the area which you can survive or where you can compete better if you can't then you you die you you are wiped out so the importance of meiosis is to bring about um variation so that now there is there is there is a survival of these organisms in the population so it is a great importance because it creates genetic diversity in the population hence difference in the survival of the organisms in the environment so basically that's what I say that it brings about what called survival from there let's look at uh what you call the the non-disjunction the consequences not disjunction and the consequences when you talk about non-disjunction you need to know where does it occur which phase we need to know the phase the phase where does non-disjunction occur so it occurs in in anaphase it can be anaphase one or it can be anaphase two and then what is the importance of this non-disjunction oh there's non-disjunction has any importance or it has the negative effect on organisms so that is what you're supposed to cover in the so we are saying that non-disjunction each nucleus should contain 200 chromosome you have to know that if it is a human cell this is a human cell that each nucleus must contain 23 chromosomes after meiosis but if now a non-disjunction occurs it means that uh if the chromosomes fail fail to separate to separate if uh chromosomes failed to separate that's what's called a non-disjunction and during anaphase if the chromosomes fail to separate then it means that this number of 23 will not be brought about so one nucleus so now what happens in non-disjunction yes okay saying that you have um a cell a sale under metaphase Mera Mera phase metaphase one and then now this cell has uh chromosomes remember they are supposed to be aligned along the Equator you see you're explaining the process of non-disjunction they're supposed to be aligned along the Equator now in actual sense in the normal cell if it is normal yes we expect it to be like in anaphase in anaphase in an office I expect it to have these chromosomes separating these chromosomes separating you see these chromosomes must separate you see they are separating and then in telophase I expect this cell to form two cells from two cells whereby these two cells they have two chromosomes you understand so if it is a normal cell I expect it to be 46 um now this one is also 46 after at the end of uh till phase one telophase telophase one I expect to be 23 and even so this one 23 but if non-disjunction occurs if non-disjunction uh disjunction occurs what happens metaphase the chromosomes yes they will be fine like that in metaphase they will do what they will be fine yes and then when they go to anaphase now we because we said it fails to separate during anaphase yes these ones are 46 if it's a human cell then automatically it's gonna be now what's gonna happen is gonna happen that the whole set the whole this this whole set is gonna go to one side the spindle fiber are going to fail to to contract from this other side you understand and then it pulls this one also pulls this one but this one is going to go on one side you see it's gonna go on to one side now this is going to result in a Cell having yes one two and then three one two and then three and then the other one is gonna have only one chromosome you understand so now it means that this one is going to have an extra extra chromosome this one is going to have an extra extra chromosome yes and then this one's gonna have short is going to be less of one one chromosome so it's gonna have an extra chromosome this one's gonna be less of one chromosome so now if this one is still 46 now this one is supposed to be 23 but it has an extra therefore is going to be 24 and then this one is supposed to be 23 but now it has is short of one chromosome it's supposed to have two chromosomes now it has three it has one extra and then this one is supposed to have two but now it is having one it means that is short of one chromosome if we go back to a human cell it's supposed to be 23 then it means that it's going to have 22. so now what happens so because now uh it has an X it has three three chromosomes then in science you're gonna call it trisom try try we call it Zone because it is a cell the body which describes a cell which has uh three chromosomes of the same kind uh on the uh three chromosomes of the watch of the same of the same kind the name here is gonna be because this one is gonna be mono mono because it's a cell a body then we're gonna call it Zoom so it's gonna call it monosome if this non-disjunction occurs on chromosome number 21 then you're gonna call it uh Price Zone Price Zone 21. we're gonna call it dry zone 21. now what happens what happens if this cell which has 24 chromosomes the trism they try Zone 21 price on 21 if it fertilizes a normal gamete for example this is a sperm and then fertilizes a normal gamete which is the ovum yes oven then automatically what you're gonna have is we're gonna have a number of them remember it has a normal cell is going to have 23. so now it's going to have uh 24 and the 23 then you're gonna have 47 remember a normal person is supposed to have 46. now instead of 46 is going to have 20 uh for sorry 47 so it means that now this condition because of an a normal uh cell fertilizing uh the cell which has an extra chromosome on chromosome number 21 is going to result in what you call uh down uh syndrome syndrome is when I result in what you call down syndrome that's how Down syndrome is being brought about however we can also have a situation because we say that uh this cell is having 22 instead of 23. so now if um if 22 if 22 fertilizes the one which is 23 yes now it means that it's gonna have for 45 instead of 46. still this is also an abnormal individual so a monosome if it fertilizes um a normal cell is going to become 45 and then a trisome it fertilizes the normal Cell It's Gonna form 47 all these results in abnormality in an individual so uh that's what we are trying to explain so now when we say that um one nucleus of uh when that's just none this Junction occurs as we say that one nucleus content will contain 22 chromosomes we have seen where do we get the 22 chromosomes it fails to separate and then uh one nucleus is going to have a 22 chromosomes of instead of 23 while the other ones will have 24 instead of 23 it means that this one is the monosome and then this is a trisome it is less of one chromosome it has an extra of chromosome when either of these resulting gametes fuses with the normal gamete normal gamete is 23 so now if um uh this fertilizes this uh 24 and 23 is going to be 47 22 and 23 is going to be 20 45 that's why they're saying that result in 45 or 47 chromosome instead of 46 which is 23 plus 22 you get 45 we have explained that and the 20 three and 24 you get 47 instead of what 46 23 plus 23 so this is this will lead to a child having what you call Down syndrome Down syndrome and then the child will have for his uh five autosomes with three uh chromosome number 21 it means that chromosome number 21 is gonna be three of them that's why we call it trisom that cell is for the try Zone because they have three chromosome number of the same kind instead of a normal pair and one pair of six chromosomes so six chromosome so if they're 25 plus the six chromosome which is X and Y or x and x based on which gender is it then it's going to become 47 and then the woman over the age of 40 I'll have a great chance of having children with their own syndrome we're not saying that uh children uh all the people who are four years and above they're gonna produce kids who are having Down syndrome complications you know we are saying that the people who are four years and above they have a great chance of having this imitation have a great chance of having a baby with Down Syndrome I think you have ever seen people with a Down Syndrome have you ever seen them so what are some of the the the the the the characteristics of people having Down syndrome stocky body the body is talking uh flattened face with small and broadness small skin yeah you you you have ever seen these people uh let's look at a picture which has a Fall Down syndrome here so uh the falls in the inner corner of the eyes that appear to be slanted upwards and then um a large tongue these kids they have large tongue actually the tongue is always protruding out yes with the small eyes actually the eyes are tilted yes and then you're saying that they blow the hands the hands are big and short they're actually fingers they're big and short they're broad big and short and then you're saying that uh wide space between the first and the second tall if you check the you may not see the the the the the kid because of the shoes all right but if you get a chance uh this kid to remove the shoes you can see exactly what is happening yes so now let's look at some of the differences one analysis to here we say that we explain this that if you wanna know what the differences between meiosis one and meiosis two just look at the phases prophase what happens in prophase there is no crossing over there is crossing over there is in in my metaphase uh chromosomes align along the Equator randomly in homologous pair chromosome line along the Equator singly so and then anaphase chroma homologous chromosome separate to opposite poles while the other one chromatid is separate therapies you form two chromosomes sorry two cells the other ones you form four cells crossing over occurs in profits there is no crossing over so you have to look at the phases okay chromosomes align along the Equator in homologous pair you see the word homologous in the homologous this is the key point in the homologous pair then the other side the chromosomes align along the Equator individually this is the key point to which which which which um differentiate them then they are saying that the chromosomes move to opposite poles they move to opposite poles they are not saying they're saying chromosomes it means that uh the way a chromatids now sorry homologous chromosomes so the chromosomes now they move opposite part what moves to opposite poles in terms of uh meiosis too is there chromatids chromatids uh move to opposite to opposite poles yeah why do you call them data chromosomes they have not yet developed to form real chromosomes that's why we call them data chromosomes but we prefer saying chromatids two cells from uh two cells form at the end so we say that here you form two cells where the other side you form four cells you see the key Point yes and then our chromosomes number in in meiosis one is halved chromosome you have the halfing here you have the halfing event you can't see because of the color and then decide uh the chromosome number is maintained it means that you start with 23 and then you end up with 23 yes then uh crossing over takes place we say that there is crossing over while the other side there is no crossing over there is no crossing over basically those are some of the differences between meiosis what about the similarities do they have uh do we have some small businesses and mitosis yes obvious there are some uh similarities what are some of these methods both process involve division in meiosis one you have what's called a cytokinesis even in mitosis you have what's called cyto cyto cyto Kinesis division of division of the nucleus so both cells you have a new you have cell division it means that new cells are formed however in meiosis you form four cells and then in mitosis you form two cells which are identical both process occurs in M phase M phase is a phase whereby the the cell starts to divide the the cycle is divided is divided into M phase you have uh the the G phase one uh the S phase and then the G phase two this all this is interface interface that's why you call recall that this is not a part of meiosis and I can call this uh growth uh sorry growth phase growth one synthesis grows two and then this is uh where there is a division the real division which is taking place actually it it takes around 80 minutes minutes for it to to to to to to happen while this one takes around uh the remaining from 24 hours that's how What It Takes yes all right in both cell cycle the stages are common you have metaphase prophecies anaphase and telophase both in meiosis and in in in in in uh mitosis the synthesis of DNA both you'll find the seasons of DNA in interface you see here in the in the S phase which you call synthesis that's where you find it the organelles and DNA are being synthesized from cytokinesis division the vision of the of the cytor cytoplasm yes cytokinesis occurs in the two cells what about the differences between mitosis and meiosis difference between mitosis and meiosis okay uh here we see that it occurs is in the cell body uh what you call the somatic cells well this one occurs in ovaries and testis resulting in gametes production of genetical identical these ones are identical The Identical word these ones are genetically different they are genetically different this one results in two data cells uh while this one results in four other cells these cells must undergo maturation interface so that they can mature so that they reform what you call real cells you've got them daughter cells because they're still young then you have one nuclear division you don't have mitosis one and mitosis two no so it means that the nucleus device once that's why we say one Nuclear One nuclear well here we have two nuclear division uh here we have uh crossing over takes place in prophase one while here crossing over takes place there's no uh there is no crossing over in in prophase one that's why they're always identical well in meiosis there is crossing over which takes place in prophase one then here we said that it results in dollar cells being deployed you started with the diploid you start with the deployed to end you end with deployed to end while here I start with the deployed to end and then you end with a haploid one end you see yes then here results in the somatic cells where this one results in the gametes so basically uh those are the differences between meiosis and mitosis so now let's look at so I think our next class solicit to be a reproduction reproduction we're going to look at the reproduction I know that many people like this topic and then even in my uh sorry Even in our new YouTube channel for bright doctor we're gonna also discussing too much of reproduction yes check the link below don't forget to subscribe and like and also share to others so that they can also benefit from our our classes thank you very much see you again foreign [Music] [Music] please use the link below to get the notes questions and other videos don't forget to subscribe like and share to others for our daily new videos yeah well others for our daily new videos yeah welcome back guys welcome back to our class we are looking for distinctions and making sure that we pass all of us we must pass we must go to the university yeah I've got the vote Yes today we are going to be looking at what you call um meiosis I know meiosis is one of the difficult topics very simple to take to grasp but try to answer your questions let's look at meiosis meiosis we said that meiosis human reproduce or other organisms they reproduce they multiply what about cells cells they have two kinds of uh reproduction they undergo they have what's called mitosis and you have what you call meiosis my my process can occur in other body cells but meiosis occurs only in the reproductive cells where did you come from actually meiosis was the basis of you living without meiosis you then have existed so let's look at meiosis in detail so it's a type of cell division that results in four data cells each with half number of chromosomes through that of the parent so it means that meiosis starts with the uh it starts with the one cell this cell divides and then you form four Dora cells these cells they have half the chromosome number to that of a parent if you have started with the four chromosomes it means that uh the these cells will result in two chromosomes that's why you're saying that half the chromosome number of that of the parent if the man yeah the badasser is having 46 chromosomes then the the reproductive cells or the daughter cells which are resulting from that are going to be having 23 and then from the mother also 46 they're going to result into 2.3 so the process of reducing these cells into half the chromosome number that process or that reproductive process is what you call meiosis so what does meiosis result in so this message will result in the production of gametes gametes these are these palms and the over and talk when you're talking about the humans and then plants you're talking about spores in the pollen grains you can talk about the obvious those are some of the things uh which as a result of of meiosis so in humans or in animals it occurs in the ovary you see this colored word in the ovary and then these ovary they produce what you call the over so the reproductive cells in the film in the females we call them over if this one is probably over if there are many you call them over and then uh in in male in male because it is occurring in testis and then testis uh what we call we call them spermatozoa the cells which are being produced you call them spermatozoa so in female we call them ovary those are the over raised ovaries produced over and then in in testis uh they produce what's called a spermatazzo what about in plants in Plants occurs in the ovary still but what it produces over reproduce what we call the obvious meiosis occurs in the anthers and then what it is being produced is what you call the uh the Polynesian so the question can come and say that um other than the ovary in animals which other place does uh meiosis occur that is testis and what does it produce it produces what we call this spermatozoa and then in in in in plants uh it occurs in the ovary it produces what you call the obvious basically uh that's what you need to know about this first introduction of of meiosis you know meiosis is basically the cell divides and the the most important thing to divide is the nucleus so so we need to know the nucleus to do a recall about the nucleus because we saw the nucleus at the beginning of DNA and also saw the nucleus in the grade 10. so let's look at the nucleus the centralizome and then the cytoplasm nucleus contain the genetic material what about inocytominees uh cell and then plus means a fluid the fluid of the cell so basically this is what you are going to look at let's look at them in detail so this is a cell it has a nucleus outside you have what's called a cytoplasm then in the cytoplasm you have what called the centrosome centrosome why do we talk about the nuclear centrosome and discipline because uh uh this uh the DNA you'll find it there and then it is the centrosome which which produces the centrioles and the centrioles spindle fibers which hold the chromosomes in position that's why I talk about it and then there is a time when this one disappears and then you remain the content of the cytoplasm so the nucleus disappear and then remain only with the content of the cytoplasm so basically that is a nucleus and then when it brings it in exam it looks like this so this is a nucleus it's a nucleus but the nucleus has a density body which we call the nucleolus nucleolus then outside the nucleus if you have the nuclear membrane which has the extensions extension which you call the endoplasmic reticulum but because it has the ribosome they look rough then we call them the rough endoplasmic reticulum the rough endoplasmic reticulum so basically uh that's it it has the nuclear power the holes where substances go through almost especially messenger RNA in this case and other substances then it has what you call the nucleoplasm the nuclear the plasma of the nucleus meaning that the fluid of the nucleus the nuclear envelope that's what you call the nuclear membrane then the ribosome we say that the ribosome that sites for protein synthesis chromatin this one is done which condenses to form chromosomes and then you have the nucleolus so we have explained all that so when you look at the nucleus or when you look at the DNA basically that's what you see you have when the chromatin Network condensed you from what you call the chromosome so the chromosomes uh they condense you see they have condensed and then after that you form the real structure of a chromosome it looks like this so that's the structure of a chromosome now let's look at the chromosome in detail so we have seen where the chromosome come from it cannot exist without DNA with this specific genes you see it has specific genes so let's look at the structure of a chromosome why do we need to look at chromosome will you resemble your father because of the chromosome because of the genes you or obtained from your parents your father your mother what about those who don't resemble the father and the mother but they resemble their grannies we shall see another question what about why so in this topic we're gonna see why why do you resemble uh your neighbor why do you resemble when you go somewhere when you go somewhere someone can say that we're not you resemble someone why do you resemble someone those are some of the questions we are going to answer and this is the reason why we need the structure of the chromosome so the structure of the chromosome chromosomes as thread-like structures present in the nucleus the thread-like the thread-like it means that they are like strings centralized structures found in the nucleus that's why we talked about the nucleus which carry genetic material that's why you resemble your father that's why you resemble your mother which carry genetic material from one generation to the Next Generation so it means that your kids will try to resemble you yes then you're saying that each chromosome is made up of the DNA we saw this that DNA genes are almost the same thing but on a different scale so this DNA or these genes are tightly coiled many times around a protein called histones so the histones we saw this when we are talking about uh when you're talking about uh protein synthesis and also the when you're talking about the structure of the DNA yes so they they coil around to format called the histones that supports the structure of the DNA because the genes cannot just exist there in in in in air they they need to have a support so the support which uh the support we call it them histones so these are the support which make the DNA strand to stand or to be where it is and so that the chromosome can be formed when this DNA condense all right this is the structure of of of chromosome before remember we talked about during DNA replication that when does it occur we say that it occurs before the cell divides or before meiosis so before the cell divide the chromosome will look like this yes they will look like this therefore we call this one single stranded chromosome chromosome one chromosome sometimes we call them unreplicated chromosomes they have not yet done DNA replication but the moment DNA replication occurs this chromosome is going to change from this format to this format that's why we say that it doubles the chromosome number don't say that it increases the chromosome number it increases the chromosome number it increases the genetic material from what to what the best answer is to is double the chromosome number doubles the chromosome number so that when it was like this then it becomes like that so uh this is the centromere the center of the chromosome we call it centromere the two chromosomes which look alike it means that uh they share the same structure yes and the position of the genes on them then we call them homologous chromosomes homologous chromosomes so one chromatid from one chromosome and another chromatid from another chromosome because they are homologous chromosomes therefore because we are talking about chromatids of homologous chromosomes then they are going to become homologous chromatids why because we say that they are coming from homologous chromosomes but each part is a chromatid therefore they become homologous chromatids so um so sometimes as I say that this is called unreplicated chromosomes and then we call these ones they're replicated the chromosomes or what you call homologous chromosomes so each of these have has two names and they replicated chromosomes or single standardic chromosomes and then these ones double-stranded the chromosomes or replicated chromosomes so the number of chromosomes in each cell is a characteristic of organisms for example humans we have 46 chromosomes you'll find out that glossophilamenton gasta has eight chromosomes you find out that the ship has over 60 chromosomes so each organism has a specific number of chromosomes it has and you might find out that the biggest organism has fewer number of chromosomes so that's how life or how that's how God is uh so it doesn't matter whether you are big or smaller but you might have your own uniquiness that you're saying that chromosomes which are single thread become double when the chromatid joined by Central mayor so the center of the chromosome we call it centromere as a result of DNA replication so if DNA replication occurs as we said now the single stranded chromosome are going to become double stranded so that's why you call it unreplicated chromosome or single strategic chromosome the moment DNA replication occurs it becomes double-stranded chromosome or replicated chromosomes yeah so what are some of the difference between uh the haploid and diploid higher die means to employee means you are describing your body yeah so help me half means it is derived from the word half half the chromosome number if a human being is supposed to have 46 chromosomes so when you are haploid or with the structures haploid because they have the chromosome number of that organism for example if organism has 20 they haploidy state of it is going to be 10. if the organism is having uh 32 the haploid number uh of that uh organism or haploid state of that organism is going to be 16. so haploid means half the chromosome number deployed means doubling doubling what does mean where is the double there it means that half from the father half from the mother and then they double it when they double then they format because they diploid or deployed the way you uh pronounce it so haploid is the quantity of the cell or organism having a single set of chromosomes they have what's called a single set of chromosomes so if you have chromosome number from one to two from chromosome number from one to ten these chromosome numbers this chromosomes must be in pairs so if you are haploid chromosome number one to ten they will be in single single single there will be one one one one they want to be in pairs so that's what you call it haploid but if it is deployed is when the cell organism has a pair or two set of chromosomes paired or two sets of chromosomes one from each parent it means that one from the father one from the mother when they combine because there are two organisms contributing this then you form the word die which is um two and then employee means yes it's a state which you describes organism with the pull set of chromosome one from the father and one from the mother that's the meaning so for sexual reproduction to take place sexuality means that it must include the gametes it must include the gametes and must include the sex reproduction to take place yes what happens uh a haploid metal gamete that is if we are talking about humans we're talking about sperms will fuse with the haploid that means that it will refuse what is a haploid metal gamete half of the chromosome number from the male the government would have half of the chromosome number from the male if the male is 46 the gamete is going to have or the sperm is going to have 23 chromosomes will fuse with the haploid number from haploid from the female also now the female is going to produce 23 when they fuse together you form fertilization so when they fuse together that process is called fertilization now you form what you call a diploid because half from the father half from the mother then because it's half half from different people then it becomes die becomes two they fuse together and then um when you're talking about fission overallization we are not talking about sex because there is the vision of fertilization can take place without sex meaning that how many maybe they used a male just give out their sperms so when you're talking about fertilization we're talking about sex has already occurred and then the sperms they swim along the female reproductive system and then Fusion will take place this Vision can even take place someone had sex at night and then you're walking on the street Fusion is taking place imagine what did you know when when was your fertilization took place you don't know if any opinion doesn't know okay those are the wonders of the science all right if you need more questions concerning about this reproduction go and visit our YouTube channel which you call Bright Doctor Bright doctor I'll give you the link in the description below so that you can understand it better all right the result is a diploid zygote the result is a deployed zygote so when you have the haploid haploid you form a diploid or a diploid zygote so it means that when the sperm fuses with the oven you form what you call a zygote but this zygote has a deployed number of chromosomes this body has a deployed number of chromosomes it means half from the father half from the mother all right haploid half which is indicated haploid is indicated as one end and then diploid is also indicated as one sorry haploid from the mother one end for example haploid from the father for example is also one end so when you combine them you form the diploid which is all yes is is the hall now half and half you get hot yes basically half from the father half from the mother from the diploid that I mean is true meaning that contribution from one person and information contribution from another person so because this resultant uh body is having two contributions then we call it a diploid so it is indicated as to n we shall be using this language so you have to know when someone uses this language you must know what it means so is zygote is where efficiency develops from we shall see in the videos we're gonna be releasing soon uh uh how is the zygote form you see the spam of swimming after after sexual after sexual intercourse you see this sperm swimming going to the over manifestation takes place for more detailed about this visit what you call the bright Doctor Bright doctor uh just a link below drop your question then we shall give you the answers on that YouTube channel but for purpose of passing exams we don't go far away from this but there we can describe as much detailed as you want so uh sexual sales is I.E that is palms and other are haploid so we call them haploid they're one end 23 chromosomes in humans so it means that the other organisms have different chromosomes so we have what we call the somatic cells so it means that you have two types of cells we have what called the six cells those are the gametes I say that meiosis can only take place in these cells we don't find meiosis in any other cells only in the gametes so you have the other body cells some some some some comes from the word SoMo which means a body yes so these are body cells are diploid which means that they're 2N if they are 46 it means that the haploid is going to be 23. but the question when it comes it does not bring only human you can only talk about 46 if they have specified in the question that this is a human cell because they can bring yourself with the 10 chromosomes they can bring yourself with four chromosomes if they don't specify that this is the human please don't use it for a six because the question is not asking about humans there you have the 23 pair of chromosomes that result in the zygote are divided as follow how number 22 pairs these are the number of chromosomes we have in the body 22 pairs that is from pair number one to pair number 22 we call them orosomes autosomes it remains that how many chromosomes we have 44 because this is a pair pair number one appear number 22 we call these ones Horizons one pair of six chromosomes that are one pair that is the 23rd pair we call it six chromosome or scientifically we call them gonosomes scientifically we call it gonosomes so this pair is divided into two we have what's called The xx which is female and then we have X Y which is male so it means that um females always they will have XX and males will always have X Y ah there is a questions which is supposed to be posed here why if if if if females are XX and the males are X Y it means that it's the mayor's to determine the sex because female have X also male has eggs but female don't have y but male have y so it's the male two males to determine the sex of the human being the sex of an individual so males you must stop you must stop saying that ladies are only giving you females they're only giving you boys they're only giving you girls say I'm giving myself boys I'm giving myself girls it's you who is determining this however there are some other factors which also determine it can be on the side of the female for more details this is the bride doctor drop your question there we will be able to answer those questions if you drop the question there then I'll be able to answer those questions and humans have what we call the chromosomes from we say that from chromosome number one to chromosome number 22. these chromosomes are arranged in a specific order and they appear in a specific way they they are in pairs and then they describe different characteristics in the organism so let's look at the karyotype the the composition of the nucleus which kind of nucleus which kind of nucleus do you have the chromosomes the type cardio is is is derived from the nucleus and the type so which type of the nucleus do humans have thus derive the name of Cario type humans sell America Forex chromosomes it means that our nucleus uh have 46 chromosomes and then this is 46 chromosome are arranged in pair these chromosomes are arranged in pairs it means that they cannot exist as singers what does this mean if you're not married all right it means that they are arranged in pairs each pair is different from each other or each pair is different from other by so this this these pairs are different by how do they differ how do they differ they differ by shape size and genetic composition so pair number one is totally different from Pair number two by size shape and the genetic composition it means that what pair number one determines is not the same thing what pair number two determines for example you'll find out that chromosome number 23 pair number 23 will determine the sex you cannot find this in other chromosomes so they vary in shape size and the genetic composition from Pair number one to pair number 22 number 1 to 22 are called autosomes what about 20 30 pair is called gonosomes which has x x for female and the X Y for male X you have to know this x is longer and bigger over y why X is longer and bigger over y question why why is X longer and bigger the right doctor will answer that but on the purpose of this um X carries more genes compared to why compared to y so so so a care you type an example looks like this you see that chromosome number pair number one number two number three number four they they vary in appearance shape and also they vary in the genetic composition so from 1 up to 22 we call them all this we call them gonosomes we call them autosomes and then the 22nd pair we call it Gunners so basically uh does it uh the vision of the process of mitosis it's not it's advisable before you start meiosis to do a revision concerning about concerning about the process of mitosis so guys our next video as we say that we're gonna be having uh prizes air time uh meals yes we send you a vulture and then you buy whatever you want to buy it can be a school bag t-shirts we have a lot of gifts to give out on our YouTube channel so please don't forget to subscribe don't forget to subscribe like share so that others also benefit from this content and then we're gonna be having all these subjects so we are trying to increase this so mitosis occurs in every living organisms in the somatic body cell to produce those are the body cells other cells other than sperm and ovum to produce genetically identical cells so you can have a hole on the mouse on on the cheek and then uh you need meat so what they can do they can cut the bum and then they put on the mouse and you move with the bum or or or on your face basically why why do they do they do that because these cells they undergo what's called mitosis they are genetically identical they are genetically identical they meet from your bums is exactly the same as the meat from your face in terms of the genetic composition so two identical cells are reproduced two identical cells are produced with a identical chromosome number equal to the original cell it means that the parent and the babies or the daughter cells they're exactly the same there is no difference that's why when you get your wound another meat develops those cells which develop the exactly the same mitosis has only one cell cycle I it doesn't have that that mitosis one animal it only has one cell cycle only one silver cycle it means that meiosis when on on the side of meiosis it has two cell cycles meaning that it has meiosis one and also has meiosis two so guys let's look at the process of meiosis yeah the process of meiosis was a very good introduction of of meiosis now let's look at meiosis in detail and this will be our next topic tomorrow don't miss it don't forget to subscribe like and then share the video we will be having gifts uh prizes in the our next videos starting from meiosis thank you very much and also don't forget to like subscribe and share our new YouTube channel in the link below called the bright doctor anxiety was giving me a lesson thank you [Music] [Music] [Music] please use the link below to get the notes questions and other videos don't forget to subscribe like and share to others for our daily new videos yeah welcome back guys welcome back we are today you're going to be looking at what you call the process of meiosis so we saw the introduction of meiosis and today we'll be looking at the detailed process of meiosis and where most questions come from in examination yeah don't forget that we say that in this video we'll be having some some gifts some gifts for those people who are watching the process of masks don't forget that we say that mercies is the process whereby one cell divided to form four daughter cells these cells are genetically different from each other and from the parent the process of meiosis we say that a type of cell division that results in photo other cells uh Excel with half the chromosome number to the parent so message is a continuous process it's a continuous process but it divided into different phases and and and events so the events um for example the first event is what we call the interface interface is a is not part of meiosis you uh you must know that interface is not part of meiosis it's just a growth phase because meiosis is regarded as a reproductive uh process in the uh reproductive cells with a determining the the cells which you call the gametes so um it includes a DNA replication that's where where DNA replication takes place remember when you're talking about DNA we asked a question where does it occur we said in the nucleus when does it occur occurs before the cell divides or it occurs during interface So when you say before the cell divides it means that uh interface is not regarded as a phase of meiosis it's just a growth phase it's like saying that you give us a baby and then a baby immediately cannot give birth to another baby need some time for this baby to grow so that now uh once the baby grows then is ready to reproduce when the cell divides and then goes to the last phase it does not divide immediately no it requires some time for it to grow so during that process of growth is what we call interface and the things which occur in that phase some of them is DNA replication doubling of the DNA chromosomes which are single-stranded they become double we saw it that we have what we call the unreplicated chromosomes when they double they become the replicated chromosomes so when the the chromosome has one thread then we call it uh an unreplicated chromosome or what you call single standard chromosome but when it becomes a double as we said as you see it here it becomes what it it is called uh replicated chromosomes or double stranded chromosome so each chromosome will consist of two chromatids joined together by a centromere so a chromosome it must have a chromatid it must have a centromere joining it if it is replicated the chromosome it will have two chromatids and these chromatids must be joined together by a Centro mere centromere is the middle part of the chromosome then um DNA replication what happens in DNA replication DNA replication helps to double the genetic material to double the chromosome number as I said that we don't set increase the chromosome number as we ask a question it increases the chromosome number from what to what so we need to say that it doubles the chromosome number of genetic material so the material so that genetic material so that it can be shared equally by the new cells arising from the cell division it means that now these cells the new cells which are going to be formed they're going to have the content they're going to have the content they're going to have the chromosomes they're going to have other cell organelles equally shared equally because each cell must have this content so if it doesn't have then it means that it will be empty and then you won't be able to survive so it is the function of interface the growth phase uh to bring about the doubling of these organelles and the doubling of the genetic material so that each cell each cell has a equal amount of the genetic material and also the cell organelles if we have said that our interface is not the part of meiosis then what are the phases of meiosis number one we have what we call the prophase number two we have what we call the metaphase number three what we call the anaphase number four we have what the telophase and then we go to Professor to profase metaphase two anaphase two Terra phase two so we are talking about uh prophase metaphase anaphase what is it what does it mean prophase means preparation Pro means preparation P versus P then you have metaphase versus middle m versus m and then anaphase versus apart a versus a and then t means still phase T versus D so even in prophase two the metaphase two anaphase two and enter of phase two so we form a if you take the first letter we form what called ipmat This is in different color it means that this in interface is not part of meiosis that's why we don't have interface one and interface two we only have interface so it means that it's not a part of meiosis so the the the the process of meiosis begin with prophase metaphase anaphase and therapies whereby we say that this is a preparation middle apart and then they have reached the what's the terminal what are those things which we are talking a middle about terminal what are they we are talking about with the chromosome as you see them here so this is trying to show you exactly uh what is happening so it means that you start with one cell the one cell divide from two cells and then these two cells divide from four cells but actually what is really happening for this cell to divide is what you're going to look at in the details of each phase let's look at meiosis one meiosis is divided into two phases into two divisions not phases the first military division and the second magnetic division so in the first metric division it will have prophase one metaphase one another phase one two phase one and then the second metric division we will have uh profits to metaphase to another phase two and then turn off phase two so the market the first meiosis uh this is called a reduction division whereby when we talk about reduction division you start with 46 chromosome at the end of mouse is one you end up with the 23 chromosomes 23 chromosome in itself hence we call it a reduction division this division results in the reduction of the number of chromosomes from 46 um to 23 in each cell so uh the resultant gametes are haploid it means that they have one set of chromosomes from chromosome number one chromosome number 23 they are not paired it means that they are single haploid half it means that the cell has 23 chromosomes you know it's 23 pairs of chromosome all right let's look at the phases of of of meiosis the first phase is prophase which means preparation the cell is preparing for whatever is going to be uh doing so the first thing is chromatin Network we say that chromatin Network means that uh uh entangled entangled DNA DNA is in form we don't have a direction when we look at it we don't know where it starts or we don't know where it ends so it is chromatin Network when it condenses it forms it becomes thick when it becomes thick it forms what's called a chromosome so the chromatic Network condensed when they condense it means that now that it has formed the chromosome now these chromosomes the chromosome which look alike homo which means the same logos which means structure so it means that chromosomes which look alike chromosomes which look alike they are going to come together that's why you're saying that homologous chromosomes are formed it means that the chromosomes should look alike they come together when these homologous chromosomes the way you see it here when they they they they they they they they come together they cross over what do they use to cross they cross using the chromatids the one chromatid of one homologous chromosome crosses with another chromatism of another chromologous chromosome and then the process continue so the spindles already starts to form it means that now the spindle fiber they start to form and then once they start from the nuclear membrane starts to disappear let's look at the diagram here so you see that here um the the the the the chromosome they condense the homologous chromosome you see this one is short this one is long so this shot cannot go with the long one no the shot goes as well the shot the long one goes the the long one that's the principle this these chromosomes they come together and then the chromatids they cross each other when they cross each other we call it crossing over that's why we're saying that crossing over takes place and then the point where they cross over we call it chasma we're going to look at this in detail and then now this window they start uh the same rules they start to move to opposite poles as they move yes as they move they spindle is 32 form so once you see something like this they have crossed like this then you just know that yes this is is profits why because the chromosomes are crossing over homologous chromosomes are crossing over we don't have crossing over anywhere else except in prophase one no even not in prophase two we only have it in Phase One why in Pro phase one because the chromosomes are still in homologous pairs let's look at the process of crossing over so we have seen that the homologous chromosome the chromosomes which look alike they're going to align together when they line together one chromaterial of each chromosome overlap so it means that they cross each other when they overlap these chromatids they must be overlapped based on the homologous pattern for example it means that the one chromatid form one homologous chromosome and another chromatid form another homologous chromosome they cross over and then when they overlap and they cross over it means that they cross over at a point called chasma and then crossover takes place at a point called chasma if it is one with chasma if there are many you call them just matter so when we say chasma or chiasma burning on the kind of English you are using then um chasma or chasma is is is is is one is a point where these two homologous chromatids cross over during prophase one and then now the chromosomes separate so it means that now they have formally different chromosomes I always ask this question to to different people are you sure your father is your father why am I asking you that you don't resemble him actually you don't even resemble your mother you walk you go somewhere and then you find out that you resemble someone why and they ask you that hey when are you resemble someone I I know that why basically he might be your father but because of crossing over this made to the exchange of the genetic material if you came from the same father same mother you breastfeed on the same breast of your mother why don't you look alike it means that this crossing over this process of meiosis helps in bringing about variation among organisms so it is a very important process to make humans individuals different from each other and then this helps in the survival if all of us we are the same then it means that we won't be able to survive imagine everyone is rich do you think that there will be someone who is working for another one everyone has money you think I would have taught you this no because I don't need you don't need this no one would have been watching you don't need this you have your money what else you want but because there is difference among these organisms among us then it brings about what God competition hence different people will work differently and in different environmental conditions so that's the purpose of meiosis to bring about variation among organisms of the same species all right let's look at continuing with the process of crossing over so these differences is being brought about by crossing over imagine a father producing uh over 100 million sperm for a single age actuation and then this sperm each sperm is different from each other what made them to be different from each other is the process of crossing over because it forms different combination of chromosomes all right let's look at so we think that you have one homologous chromosome and another homologous chromosome they come together yes when they come together they overlap the chroma homologous chromatically overlap at a point called chasma yes if you look at ABC and then inside ABC yes when they cross now this one takes this red and then the red takes the blue that's why you sit here the blue takes the red and then the red will take the what the blue this chromosomes during crossing over scientifically we call it a bivalent or bivalent based on how do you write that how do you pronounce that bivalent or be valid and then after that they separate so that each chromosome has genetically different uh each chromosome has different uh material from uh one another look if you see that ABC starting with ABC but this is a small error the small era was found on this chromosome and this is this one ABC but this one is a capital letter the capital letter came from this if you look at it here it came from the blue it means that the blue they already took the blue and then the blue took the what is the red so because of this it's gonna cause different uh gametes being formed and then if you look at it sometimes we can bring it in the exam like this uh homologous chromosomes when they cross they cross from top so when it crosses from Top it means that you have to draw it on top don't grow it down that's one of ways of of losing max if you don't show the variation correctly so you have the chromatids crossover and then the exaggerating material or the information and then now the chroma chromosomes now have new combination of the genes guys don't forget that I told you that there is a gift uh in this video just click that link below it will take you to a specific page on our website and on that page there is a code for you to obtain that airtime enjoy it when you get it when you load it on your phone let us know that you got it thank you very much let's continue and then you're saying that the second phase is metaphase one metaphase one mirror means middle it means that now the chromosomes are always in homologous pair homologous chromosomes randomly align along the Equator along the Equator of the cell in plurals it means that they they align along the Equator in two rows one um from chromosome one chromosome number one chromosome number 23 another one is from chromosome number one to chromosome number 23 that's what it means each chromosome is attached to the spindle uh the spindle uh thread from each pole this is what I'm trying to say so they align in two rows you see this is the Align in pros and then these chromosomes are being held by the spindle see each chromosome is attached uh uh to the spindle threat from each other they do this they do this Arrangement randomly so the key point is homologous because they're in pair and then each other you see this one cannot come here no they must be together like this homologous chromosomes yes it is a key point and then they they come here randomly remember we have print repairs but we're just showing you two pairs yes they are here randomly so it means that another one can be yeah this one can be on top so this set can be on top this one can be down or this chromosome can be decide this one can be decide that's what we call randomly so when they separate we're gonna form different cells so each chromosome is attached to the spindle fiber or spinozade from each pore that's what we are trying to show you that is threads are attaching the what the chromosomes from each pole so after that once they are done with this then they start to move apart which you call anaphase so in anaphase the spindle is already shortened they try to pull when they shorten they pull it's like when you your body builder when you carry something the muscle is shortened when they shorten they pull yes so they pull uh the homologous chromosome to opposite talls and then the chromosomes what happens to the this chromosome the homologous chromosome pair then they do what they they separate the chromosome of the chromosomes of the homologous pair they separate it means that now they move to opposite poles this is what is happening so now they move to opposite poles and then now uh when they move to opposite poles now they reach the pole so in telophase each chromosome or chromosome reach at the poor of the cell and then once they reach the part of the cell the cytoplasm and the cell membrane divide when the cytoplasm and cell membrane divided that process is called cytokinesis we call it cytokinesis the vision of the cytoplasm and then the two haploid cells are formed to haploid cells are what are formally and then the nucleus the nucleus or the nucleolus that dense body in the nucleus they reform then it reforms and then lastly the new nuclear membrane forms and then now they cell appears to be a full cell so this is uh what I'm trying to say yeah so now you have a form of two cells now these cells cytokinesis took place and now this is the nuclear membranes that will reappear and then the cell goes back as if it is in profits so now when it reaches there now now each cell each of it it will undergo meiosis too it means that now this one is going to go under meiosis two even this one is going to go undergo my system so that you form two here and two here so when you add them you form four cells so when you go to meiosis II what happens now prophase two you go to prophase two when it's meiosis two profess it becomes prophase to etymas they too must be there if you don't write it there we won't give a mark because we don't know which prophase is it so prophase two what happens the nucleolus remember we said that it it appeared they reappeared so now the nucleolus and the nuclear membrane they disappear again but now here we don't have crossing over so the new uh spindle fibers are formed yes they start to form and then the chromosome become visible it means that they condense and then it becomes visible and then now once they become visible now it's ready to undergo metaphase they go to the middle of the chromosome uh the cell so now you see it idea now it is forming like this and then now they are ready to move this this thing to attach themselves to the chromosome but now we don't have homologous chromosomes we have chromosomes which are not homologous it means that the crossing over cannot take place because it already took place before before yes so now uh in a metaphase two the individual chromosome line up here individual of one chromosome aligned along the Equator singly or individually so the other side we say that chromosomes align along the Equator in homologous pair and then randomly here they align along the Equator singly or individually so you have to know the difference so sometimes you ask you the difference in my usage one animals is two you can use the process to differentiate between the two so at the equator of the cell with the centromere attaching the spindle fiber or Central May attached to the spindle fiber and then now uh this is the picture if you rotate it you will see that these chromosomes are in the middle you see the in the middle if this is the pole and this is another pole they're in the middle so this one becomes the equator remember I say that equator is an imaginal line it's an imagined line it's a line which we just imagine but the line is only there is a marginal line which divide the cell into two equal parts the same thing equator of the earth marginal Line running from east to west and dividing the earth into two equal parts we're just imagining but the line in actual sense is not there we just imagine that that's the center of the Earth so we just imagine that's the center of the cell so in anaphase once they're in the middle they now they have to separate to opposite poles so in anaphase two you have spindle fibers start to form so the spin of fibers they contract when they contract it means that now they pull the chromosomes apart but now because they are single chromosomes they are not homologous now is this the the the the the the chromatids which are going to separate remember chromosome is divided into two chromatids now the one chromat is gonna go one side and another chromatid is gonna go to another side of the cell so this is what I'm saying that now the chromatids move to opposite it was together here now this one pulls it inside and this one pulls this side check the direction of the it's not facing this way is facing that way because the force of pulling is coming from the side so that's why it's supposed to be like that when you're drawing make sure that you are you take caution when you're drawing it so that you draw it properly and it's checked about the shadings also the shadings are very important when you are doing it the Dora chromosomes reach the poles once in in telophase II in telophase 2 the dollar chromosomes reach the policy when they reach the poles we don't call them chromatids anymore we call them chromosomes actually that's what we call single stranded chromosomes or any replicated chromosomes so it's supposed to get time so that this time allows these chromosomes to grow so that now it becomes double stranded again that's why we need what you call interface so new nucleus uh then forms it means that the nucleolus also come back what it means that it reforms then the cell membrane of this of each cell constrict and then the process of cytokinesis occurs when the cytoplasm divides now the process of cytokinesis occurs and then for haploid it must be haploid there are cells are formed and then now each daughter cell have have they have the chromosome number to that of the parent so that's why you're saying that meiosis is the process whereby one cell divide to form uh four dollar cells which are haploid or which have half the chromosome number to that of the parent and these chromosomes are genetically different because of the crossing over which took place so the daughter cells are genetically different as I've just said and then these are the cells which will form from four other cells and then you you see you don't call these ones chromatids we call them single stranded chromosomes watch out to this before you write your SBA so the importance of masses what are some of the importance of meiosis let's look at the importance of meiosis just start from there with the importance of of meiosis anxiety it's giving me a lesson thank you very much [Music] please use the link below to get the notes questions and other videos don't forget to subscribe like and share to others for our daily new videos So today we're going to look at the importance of meiosis non-disjunction how does non-disjunction bring about Down syndrome and then we wrap up with this topic and then we can start the topic of reproduction in vertebrates so that the other time you come back we can start a reproduction in human or what you call human reproduction all right importance of meiosis before we start the importance of meiosis don't forget that meiosis is the process whereby one cell divide to form four dollar cells and each cell has half the chromosome number to the parent it means that the cells which are being formed under meiosis are different so and then we we say that meiosis results in haploidy cells and these cells are specifically for gametes based on that information we can identify some of the importance of meiosis so what are some of the importance of meiosis the first one is the production of haploid gametes we'll talk about the gametes we say that gametes these are sperms and over so these sperms are haploid which means that if they are diploid if the pedestal is deployed it has 46 chromosomes now the gametes they are going to have 23 chromosomes if it is a human cell so number two is having effect of the meiosis overcomes the doubling effect how is this having effect being brought about when you talk about having effect remember uh remember that that we we started with the uh you start with uh 46 chromosome this is 46 chromosome they divide and when they divide you form uh one cell another cell and then this one also divided from another cell another cell we want to explain the effect this issue of having effect now this is 23 this is 23 this is 23 this is 23. so now it means that the sperms or over which are being formed here they're going to be uh they're going to be 23. now if you bring about um if you bring about for example a sperm fuses or fertilizes the ovum the ovum and then these are gametes remember the engineer this is 23 and also this is doing three so now when they fuse during the process of fertilization now you go back to 46. so it means that this is Fusion this is fertilization so this is the doubling effect this and this they double to form 46 but now meiosis is going to divide them now to form 23 23 so that's why here they are saying that the huffing effect this having effect this having effect is being outcomed by it by the what the doubling effect of fertilization so this is fertilization while this is meiosis so it means that this helps us to keep the the number of chromosomes in one generation to the Next Generation constantly but if this having effect was not there it means that if fertilization occurs now it would have been Now 46 46 and then you form another one which is 92 then 92 again 90 to 92 again you you form a big number so this halfing effect this um doubling effect is being out uh come by doubling effect the having effect out um overcomes the doubling effect of fertilization so meiosis results in reducing the chromosome number so we're seeing that thus maintaining the constant number of chromosomes uh from one generation to the Next Generation so now uh we are saying that um this produces number two another thing is um it produces what you call the genetic variation remember in in in any prophase one remember in prophase Pro uh phase prophase one you have a process called the crossing crossing over this crossing over it helps in in exchange of genetic materials so because there is exchange of genetic material then you will have different sperms uh we know that you produce over 300 million sperms for a per a single generation so each pump is different it's as a result of rough phases during the prophase uh in the process called crossing over so it brings about new recombinants new combination of genetic material um we are different from our sisters and brothers is because of basically uh because of the process of crossing over why is meiosis important for survival do we need uh reduce meiosis for survival or do organisms which don't under meiosis survive we need to this mouse is so that we can create differences among individuals of the same species if these organisms are known at the same then automatically it means that there won't be differences imagine I I ask you a question last time that if everyone is Rich what will happen if there is there are no differences among us if everyone is clever you don't need to read everyone has the information it means that there will be no competition so the reason why mercies is there to bring about the differences among organisms of the same species you can survive in hot environment you can survive in in cold environment you can survive and add-ons who survives in hot environment can't survive in in cold environment so it brings about that now all the the environment can be occupied by different kinds of people yes if you can't survive then it means that you have to migrate to the the area which you can survive or where you can compete better if you can't then you you die you you are wiped out so the importance of meiosis is to bring about um variation so that now there is there is there is a survival of these organisms in the population so it is a great importance because it creates genetic diversity in the population hence difference in the survival of the organisms in the environment so basically that's what I say that it brings about what called survival from there let's look at uh what you call the the non-disjunction the consequences not disjunction and the consequences when you talk about non-disjunction you need to know where does it occur which phase we need to know the phase the phase where does non-disjunction occur so it occurs in in anaphase it can be anaphase one or it can be anaphase two and then what is the importance of this non-disjunction oh there's non-disjunction has any importance or it has the negative effect on organisms so that is what you're supposed to cover in the so we are saying that non-disjunction each nucleus should contain 24 chromosome you have to know that if it is a human cell this is a human cell that each nucleus must contain 23 chromosomes after meiosis but if now a non-disjunction occurs that means that uh if the chromosomes fail fail to separate to separate if chromosomes fail to separate that's what you call the non-disjunction and during anaphase if the chromosomes fail to separate then it means that this number of 23 will not be brought about so one nucleus so now what happens in non-disjunction yes okay saying that you have a cell a cell under metaphase Mera Mera phase metaphase one and then now this cell has uh chromosomes remember they are supposed to be aligned along the Equator you see you're explaining the process of non-disjunction they're supposed to be aligned along the Equator now in actual sense in the normal cell if it is normal yes we expect it to be like in anaphase in anaphase in an office I expect it to have these chromosomes separating these chromosomes separating you see these chromosomes must separate you see they are separating and then in telophase I expect this cell to form two cells from two cells whereby these two cells they have two chromosomes you understand so if it is a normal cell I expect it to be 46 um now this one is also 46 after at the end of uh till phase one telophase telophase one I expect to be 23 and even so this one 23 but if non-disjunction occurs if non-disjunction uh disjunction occurs what happens metaphase the chromosomes yes they will be fine like that in metaphase they will do what they will be fine yes and then when they go to anaphase now we because we said it fails to separate during anaphase yes this one is a 46 if it's a human cell then automatically it's gonna be now what's gonna happen is gonna happen that the whole set the whole this this whole set is gonna go to one side the spindle fiber are going to fail to to contract from this other side you understand and then it pulls this one also pulls this one but this one is going to go on one side you see it's gonna go on to one side now this is going to result in a Cell having yes one two and then three one two and then three and then the other one is gonna have only one chromosome you understand so now it means that this one is going to have an extra extra chromosome this one is going to have an extra extra chromosome yes and then this one is going to have short is going to be less of one one chromosome so it's gonna have an extra chromosome this one's gonna be less of one chromosome so now if this one is still 46 now this one is supposed to be 23 but it has an extra the reference is going to be 24 and then this one is supposed to be 23 but now it has is short of one chromosome it's supposed to have two chromosomes now it has three it has one extra and then this one is supposed to have two but now it is having one it means that is short of one chromosome if we go back to a human cell it's supposed to be 23 then it means that it's going to have 22. so now what happens so because now uh it has an X it has three three chromosomes then in science you're gonna call it price of try try we call it Zone because it is a cell the body which describes a cell which has uh three chromosomes of the same kind uh on the uh three chromosomes of the watch of the same of the same kind the name here is gonna be because this one is gonna be mono mono because it's a cell a body then we're gonna call it Zoom so it's gonna call it monosome if this non-disjunction occurs on chromosome number 21. then we're gonna call it uh Price Zone price on point one we're gonna call it dry zone 21. now what happens what happens if this cell which has 24 chromosomes the trisome they try Zone 21 price on 21 if it fertilizes a normal gamete for example this is a sperm and then fertilizes a normal gamete which is the ovum yes oven then automatically what you're gonna have is we're gonna have a number of them remember it has a normal cell is going to have 23. so now it's going to have uh 24 and 23 then you're gonna have 47 remember a normal person is supposed to have 46. now instead of 46 is going to have 20 uh for sorry 47 so it means that now this condition because of an a normal uh cell fertilizing uh the cell which has an extra chromosome on chromosome number 21 is going to result in what you call uh down uh syndrome syndrome is when I result in what you call down syndrome that's how Down syndrome is being brought about however we can also have a situation because we say that uh this cell is having 22 instead of 0.3 so now if um if 22 if 22 fertilizes the one which is 23 yes now it means that uh it's gonna have for 45 instead of 46. still this is also an abnormal uh individual so a monosome if it fertilizes um a normal cell is going to become 45 and then a trisome it fertilizes the normal Cell It's Gonna form 47 all these results in abnormality in an individual so uh that's what we are trying to explain so now when we say that um one nucleus of uh when that's different this Junction occurs as we say that one nucleus content will contain 22 chromosomes we have seen where do we get the 22 chromosomes it fails to separate and then uh one nucleus is going to have a 20 chromosome positive instead of 23 while the other ones you'll have 24 instead of 23 it means that this one is the monosome and then this is a trisome it is less of one chromosome it has an extra of chromosome when either of these resulting gametes fuses with the normal gamete normal gamete is 23 so now if um uh this fertilizes this uh 24 and 23 is going to be 47 22 and 23 is going to be 20 45 that's why they're saying that result in 45 or 47 chromosome instead of 46 which is 23 plus 22 you get 45 we have explained that and the 20 3 and 24 you get 47 instead of what 46 23 plus 23 so this is this will lead to a child having what you call Down syndrome Down syndrome and then the child will have for his uh five autosomes with three uh chromosome number 21 it means that chromosome number 21 is going to be three of them that's why we call it trisom that cell is called the trison because they have three chromosome number of the same kind instead of a normal pair and one pair of six chromosomes so six chromosome so if they're 25 plus their sex chromosome which is X and Y or x and x based on which gender is it then it's going to become 47 and then the woman over the age of 40 I'll have a great chance of having children with their own syndrome we're not saying that uh children uh all the people who are four years and above they're gonna produce kids who are having Down syndrome complications you know we are saying that the people who are four years and above they have a great chance of having this mutation have a great chance of having a baby with Down Syndrome I think you have ever seen people with a Down Syndrome have you ever seen them so what are some of the the the the the the characteristics of people having Down syndrome stocky body the body is talking uh flattened face with small and broaden all small skin yeah you you you have ever seen these people let's look at a picture which has a Fall Down syndrome here so uh the falls in the inner corner of the eyes that appear to be slanted upwards and then um a large tongue these kids they have large tongue actually the tongue is always protruding out yes with the small eyes actually the eyes are are tilted yes and then you're saying that the broad hands the hands are big and short they're actually fingers they're big and short they're broad big and short and then you're saying that uh wide space between the first and the second tall if you check the you may not see the the the the the kid because of the shoes all right but if you get a chance uh this kid to remove the shoes you can see exactly what is happening yes so now let's look at some of the differences one animals is two here we say that we explain this that if you wanna know what the differences between meiosis one and Ms is two just look at the phases prophase what happens in prophase there is no crossing over there is crossing over there is in in my metaphase uh chromosomes align along the Equator randomly in homologous pair chromosome line along the Equator singly so and then anaphase chroma homologous chromosome separate to opposite poles where the other one chromatid is separate therapies you form two chromosomes sorry two cells the other ones you form four cells crossing over occurs in profits there is no crossing over so you have to look at the phases okay chromosomes align along the Equator in homologous pair you see the word homologous in the homologous this is the key point in the homologous pair then the other side the chromosomes align along the Equator individually this is the key point to which which which which um differentiate them then they are saying that the chromosomes move to opposite poles they move to opposite poles they are not saying they're saying chromosomes it means that uh the way a chromatids now sorry homologous chromosomes so the chromosomes now they move opposite part what moves to opposite poles in terms of uh meiosis too is there chromatids chromatids uh move to opposite to opposite poles yeah why do you call them data chromosomes they have not yet developed to form real chromosomes that's why we call them data chromosomes but we prefer saying chromatids two cells from uh two cells form at the end so we say that here you form two cells where the other side you form four cells you see the key Point yes and then our chromosomes number in in meiosis one is halved chromosome you have the halfing here you have the halfing event you can't see because of the color and then decide uh the chromosome number is maintained it means that you start with 23 and then you end up with 23 yes then uh crossing over takes place we say that there is crossing over while the other side there is no crossing over there is no crossing over basically those are some of the differences between meiosis what about the similarities do they have uh do we have some small businesses and mitosis yes obvious there are some uh similarities what are some of these methods both process involve division in meiosis one you have What's called the cytokinesis even in mitosis you have what's called cyto cyto cyto Kinesis division of division of the nucleus so both cells you have uh new uh you have cell division it means that new cells are formed however in meiosis you form four cells and then in mitosis you form two cells which are identical both process occurs in M phase M phase is a phase whereby the the cell starts to divide the the cycle is divided is divided into M phase you have uh the the G phase one uh the S phase and then the G phase two this all this is interface interface that's why you call recall that this is not a part of meiosis and I can call this uh growth uh sorry gross phase growth one synthesis grows two and then this is uh where there is a division the real division which is taking place actually it it takes around 80 minutes minutes for it to to to to to to happen well this one takes around uh the remaining from 24 hours that's how What It Takes yes all right in both cell cycle the stages are common you have metaphase prophecies anaphase and telophase both in meiosis and in in in in in uh mitosis the synthesis of DNA both you'll find the seasons of DNA in interface you see here in the in the S phase which you call synthesis that's where you find the organelles and DNA are being synthesized from cytokinesis division the vision of the of the cyto cytoplasm yes cytokinesis occurs in the two cells what about the differences between mitosis and meiosis difference between mitosis and meiosis okay uh here we see that it occurs is in the cell body uh what you call the somatic cells well this one occurs in ovaries and testis resulting in gametes production of genetical identical these ones are identical The Identical well this one is genetically different they are genetically different this one results in two data cells uh while this one results in four other cells these cells must undergo maturation interface so that they can mature so that they deform what you call real cells you've got them daughter cells because they're still young then you have one nuclear division you don't have mitosis one and mitosis two no so it means that the nucleus device once that's why we say one Nuclear One nuclear well here we have two nuclear division uh here we have uh crossing over takes place in prophase one while here crossing over takes place there's no uh there is no crossing over in in prophase one that's why they're always identical well in meiosis there is crossing over which takes place in prophase one then here we said that it results in dollar cells being deployed you started with the diploid you start with the deployed to end you end with deployed to end while here I start with the deployed to end and then you end with a haploid one end you see yes then here results in the somatic cells where this one results in the gametes so basically uh those are the differences between meiosis and mitosis so now let's look at so I think our next class lets it to be a reproduction reproduction you're going to look at the reproduction I know that many people like this topic and then even in my uh sorry Even in our new YouTube channel for bright doctor we're gonna also discussing too much of reproduction yes check the link below don't forget to subscribe and like and also share to others so that they can also benefit from our our classes thank you very much see you again foreign [Music] [Music] please use the link below to get the notes questions and other videos don't forget to subscribe like and share to others for our daily new videos yeah well others for our daily new videos yeah welcome back guys welcome back to our class we are looking for distinctions and making sure that we pass all of us we must pass we must go to the university yeah I've got the vote Yes today we are going to be looking at what you call um meiosis I know meiosis is one of the difficult topics very simple to take to grasp but try to answer your questions let's look at meiosis meiosis we said that meiosis human reproduce why are the organisms they reproduce they multiply what about cells cells they have two kinds of reproduction they undergo they have multiple mitosis and they have what you call meiosis my my process can occur in other body cells but meiosis occurs only in the reproductive cells where did you come from actually meiosis was the basis of you living without meiosis you then have existed so let's look at meiosis in detail so it's a type of cell division that results in four data cells each with half number of chromosomes through that of the parent so it means that meiosis starts with the uh it starts with the one cell this cell divides and then you form four Dora cells these cells they have half the chromosome number to that of a parent if you have started with the four chromosomes it means that uh the these cells they will result in two chromosomes that's why you're saying that half the chromosome number of that of the parent if the man yeah the body cell is having 46 chromosomes then the the reproductive cells or the daughter cells which are resulting from that are going to be having between three and then from the mother also 46 they're going to result into 2.3 so the process of reducing these cells into have the chromosome number that process or that reproductive process is what you call meiosis so what does meiosis result in so this message will result in the production of gametes gametes these are the sperms and the over and talk when you're talking about the humans and then plants you're talking about spores in the pollen grains you can talk about the obvious those are some of the things uh which as a result of of meiosis so in humans or in animals it occurs in the ovary you see this colored word in the ovary uh basically uh over a phone in a female and then these ovary they produce what's called over so the reproductive cells in the film in the females call them over if this one is probably over if there are many you call them over and then uh in in male in male because it is occurring in testis and then intestines uh what we call we call them spermatozoa the cells which are being produced we call them spermatozoa so in female we call them ovary those are the over raised ovaries produced over and then in in testis uh they produce what's called a spermatazzo what about in plants in Plants occurs in the ovary still but what it produces over reproduce what we call the obvious meiosis occurs in the anthers and then what it is being produced is what you call the uh the Polynesian so the question can come and say that um other than the ovary in animals which other place does uh meiosis occur that is testis and what does it produce it produces what we call this spermatozoa and then in in in in plants uh it occurs in the ovary it produces what you call the obvious basically uh that's what you need to know about this first introduction of of meiosis you know meiosis is basically the cell divides and the the most important thing to divide is the nucleus so so we need to know the nucleus to do a recall about the nucleus because we saw the nucleus at the beginning of DNA and also saw the nucleus in the grade 10. so let's look at the nucleus the centrosome and then the cytoplasm nucleus contain the genetic material what about inocytomeans uh cell and then plus means a fluid the fluid of the cell so basically this is what you are going to look at let's look at them in detail so this is a cell it has a nucleus outside you have what's called a cytoplasm then in the cytoplasm you have what called the centrosome centrosome why do we talk about the nuclear centrosome and discipline because uh uh this uh the the DNA you'll find it there and then it is the central zone which which produces the centrioles and the centrioles spindle fibers which hold the chromosomes in position that's why I talk about it and then there is a time when this one disappears and then you remain the content of the cytoplasm so the nucleus disappear and then remain only with the content of the cytoplasm so basically that is a nucleus and then when it brings it in exam it looks like this so this is a nucleus it's a nucleus but the nucleus has a density body which we call the nucleolus nucleolus then outside the nucleus if you have the nuclear membrane which has the extensions extension which you call the endoplasmic reticulum but because it has the ribosome they look rough then we call them the rough endoplasmic reticulum the rough endoplasmic reticulum so basically uh that's it it has the nuclear power the holes where substances go through most especially messenger RNA in this case and other substances then it has what you call the nucleoplasm the nuclear the plasma of the nucleus meaning that the fluid of the nucleus the nuclear envelope that's what you call the nuclear membrane then the ribosome we say that the ribosome that sites for protein synthesis chromatin this one is done which condenses to form chromosomes and then you have the nucleolus so we have explained all that so when you look at the nucleus or when you look at the DNA basically that's what you see you have when the chromatin Network condensed you from what you call the chromosome so the chromosomes uh they condense you see they have condensed and then after that you form the real structure of a chromosome it looks like this so that's the structure of a chromosome now let's look at the chromosome in detail so we have seen where the chromosome come from it cannot exist without DNA with this specific genes you see it has specific genes so let's look at the structure of a chromosome why do we need to look at chromosome you resemble your father because of the chromosome because of the genes you or obtained from your parents your father your mother what about those who don't resemble the father and the mother but they resemble their Granite we shall see another question what about why so in this topic we're gonna see why why do you resemble uh your neighbor why do you resemble when you go somewhere when you go somewhere someone can say that hey why not you resemble someone why do you resemble someone those are some of the questions we are going to answer and this is the reason why we need the structure of the chromosome so the structure of the chromosome chromosomes as thread-like structures present in the nucleus the thread-like the thread-like it means that they are like strings centralized structures found in the nucleus that's why we talked about the nucleus which carry genetic material that's why you resemble your father that's why you resemble your mother which carry genetic material from one generation to the Next Generation so it means that your kids will try to resemble you yes then you're saying that each chromosome is made up of the DNA we saw this that DNA genes are almost the same thing but on a different scale so this DNA or these genes are tightly coiled many times around a protein called histones so the histones we saw this when we are talking about uh when you're talking about uh protein synthesis and also the when you're talking about the structure of the DNA yes so they they coil around to format called the histones that supports the structure of the DNA because the genes cannot just exist there in in in in in air they they need to have a support so the support which uh the support we call it them histones so these are the support which make the DNA strand to stand or to be where it is and so that the chromosome can be formed when this DNA condense all right this is the structure of of of chromosome before remember we talked about during DNA replication that when does it occur we say that it occurs before the cell divides or before meiosis so before the cell divide the chromosome will look like this yes they will look like this therefore we call this one single stranded chromosome chromosome one chromosome two sometimes we call them unreplicated chromosomes they have not yet done DNA replication but the moment DNA replication occurs this chromosome is going to change from this format to this format that's why we say that it doubles the chromosome number don't say that it increases the chromosome number it increases the chromosome number it increases the genetic material from what to what the best answer is to is double the chromosome number doubles the chromosome number so that when it was like this then it becomes like that so uh this is the centromere the center of the chromosome we call it centromere the two chromosomes which look alike it means that uh they share the same structure yes and the position of the genes on them then we call them homologous chromosomes homologous chromosomes so one chromatid from one chromosome and another chromatid from another chromosome because they are homologous chromosomes therefore because we are talking about chromatids of homologous chromosomes then they are going to become homologous chromatids why because we say that they are coming from homologous chromosomes but each part is a chromatid therefore they become homologous chromatids so um so sometimes as I say that this is called unreplicated chromosomes and then we call these ones they're replicated the chromosomes or what you call homologous chromosomes so each of these have has two names and they replicated chromosomes or single standard chromosomes and then these ones double-stranded the chromosomes are replicated chromosomes so the number of chromosomes in each cell is a characteristic of organisms for example humans we have 46 chromosomes you'll find out that gross filamenton gasta has eight chromosomes you find out that the ship has over 60 chromosomes so each organism has a specific number of chromosomes it has and you might find out that the biggest organism has fewer number of chromosomes so that's how life or how that's how God is uh so it doesn't matter whether you are big or smaller but you might have your own uniqueness that you're saying that chromosomes which are single thread become double when the chromatid joined by Central mayor so the center of the chromosome we call it centromere as a result of DNA replication so if DNA replication occurs as we said now the single stranded chromosome are going to become double stranded so that's why you call it unreplicated chromosome or single strategic chromosome the moment DNA replication occurs it becomes double-stranded chromosome or replicated chromosomes yeah so what are some of the difference between uh the haploid and diploid higher die means to employee means you are describing a body yeah so help me half means it is derived from the word half half the chromosome number if a human being is supposed to have 46 chromosomes so when you are haploid or with the structures haploid because they have the chromosome number of that organism for example if organism has 20 they haploidy state of it is going to be 10. if the organism is having uh 32 the haploid number of that uh organism or haploid state of that organism is going to be 16. so haploid means half the chromosome number deployed means doubling a doubling what does it mean where is the double there it means that half from the father half from the mother and then they double it when they double then they format because they diploid or deployed the way you uh pronounce it so haploid is the quantity of the cell or organism having a single set of chromosomes they have what's called a single set of chromosomes so if you have chromosome number from one to two from chromosome number from one to ten these chromosome numbers these chromosomes must be in pairs so if you are haploid chromosome number one to ten they will be in single single single there will be one one one one they won't be in pairs so that's what you call it haploid but if it is deployed is when the cell organism has a paired or two set of chromosomes dead or two sets of chromosomes one from each parent it means that one from the father one from the mother when they combine because there are two organisms contributing this then you form the word die which is um two and then employee means yes it's a state which you describes organism with the poor sets of chromosomes one from the father and one from the mother that's the meaning so for sexual reproduction to take place sexually means that it must include the gametes it must include the gametes and must include the sex reproduction to take place yes what happens uh a haploidy metal damage that is if we are talking about humans we're talking about sperms will fuse with the haploid it means that it will refuse what is a haploid metal gamete half of the chromosome number from the male half of the chromosome number from the male if the male is 46 the gamete is going to have or the sperm is going to have 23 chromosomes we refuse with the haploid number from haploid from the female also now the female is going to produce 23 when they fuse together you form fertilization so when they fuse together that process is called fertilization now you form what's called a diploid because half from the father half from the mother then because it's half half from different people then it becomes die becomes two they fuse together and then um when you're talking about Fusion or finalization we are not talking about sex because there is the vision of fertilization can take place without sex meaning that how many maybe they used a male just give out their sperms so when you're talking about fertilization we're talking about sex has already occurred and then the sperms they swim along the female reproductive system and then Fusion will take place this Vision can even take place someone had sex at night and then you're walking on the street Fusion is taking place imagine what did you know when when was your finalization took place we don't know if any opinion doesn't know okay those are the wonders of the science all right you need more questions concerning about this reproduction go and visit our YouTube channel which you call Bright Doctor Bright doctor I'll give you the link in the description below so that you can understand it better all right the result is a diploid zygote the result is a deployed zygote so when you have the haploid haploid you form a diploid or a diploid zygote so it means that when the sperm fuses with the oven you form what you call a zygote but this zygote has a deployed number of chromosomes this body has a deployed number of chromosomes remains half from the father half from the mother all right haploid half which is indicated haploid is indicated as one end and then diploid is also indicated as one sorry haploid from the mother one end for example haploid from the father for example is also one end so when you combine them you form the diploid which is hard yes it's it's the hall now half and half you get hot yes basically half from the father half from the mother from the diploid that I mean is true meaning that contribution from one person another contribution from another person so because the this resultant uh body is having two contributions then we call it a diploid so it is indicated as to n we shall be using this language so you have to know when someone uses this language you must know what it means so a sperm of identify zygote is where a fetus develops from we shall see in the videos we're gonna be releasing soon uh uh how is the zygote form you see the sperm of swimming after after sexual after sexual intercourse you see this sperm swimming going to the over manifestation takes place for more detailed about this visit what you call the bright Doctor Bright doctor uh just a link below drop your question then we shall give you the answers on that YouTube channel but for purpose of passing exams we don't go far away from this but there we can describe as much detailed as you want so uh sexual sales is I.E that is palms and other are haploid so we call them haploid they're one end 23 chromosomes in humans so it means that the other organisms have different chromosomes so we have what we call the somatic cells so it means that you have two types of cells we have what called the sex cells those are the gametes I say that meiosis can only take place in these cells we don't find meiosis in any other cells only in the gametes so you have the other body cells some some some some comes from the word some which means a body yes so these are body cells are diploid which means that they're 2N if they are 46 it means that the haploid is going to be 23 but the question when it comes it does not bring only human you can only talk about 46 if they have specified in the question that this is a human cell because they can bring yourself with the 10 chromosomes they can bring yourself with four chromosomes if they don't specify that this is the human please don't use 46 because the question is not asking about humans there you have the 23 pair of chromosomes that result in the zygote are divided as follow how number 22 pairs these are the number of chromosomes we have in the body 22 pairs that is from pair number one to pair number 22 we call them orosomes autosomes it remains that how many chromosomes we have 44 because this is a pair pair number one appear number 22 we call these ones Horizons one pair of six chromosomes that are one pair that is the 23rd pair we call it six chromosome or scientifically we call them gonosomes scientifically we call it gonosomes so this pair is divided into two we have what's called The xx which is female and then we have X Y which is male so it means that um females always they will have XX and males will always have X Y ah there is a questions which is supposed to be posed here why if if if if females are XX and the males are X Y it means that it's the mayor's to determine the sex because female have X also male has eggs but female don't have y but male have y so it's the male two males to determine the sex of the human being the sex of an individual so males you must stop you must stop saying that ladies are only giving you females they're only giving you boys they're only giving you girls say I'm giving myself boys I'm giving myself girls it's you who is determining this however there are some other factors which also determine it can be on the side of the female for more details visit the bride doctor drop your question there we will be able to answer those questions if you drop the question there then I'll be able to answer those questions and humans have what we call the chromosomes from we say that from chromosome number one to chromosome number 22. these chromosomes are arranged in a specific order and they appear in a specific way they they are in pairs and then they describe different characteristics in the organism so let's look at the karyotype the the composition of the nucleus which kind of nucleus which kind of nucleus do you have the chromosomes the type cardio is is is derived from the nucleus and the type so with type of the nucleus do humans have thus derive the name of Cario type humans sell America foreign have 46 chromosomes and then this is 46 chromosomes are arranged in pair these chromosomes are arranged in pairs it means that they cannot exist as singers what does it mean if you're not married all right it means that they are arranged in pairs each pair is different from each other oh each pair is different from other by so this this these pairs are different by how do they differ how do they differ they differ by shape size and genetic composition so pair number one is totally different from Pair number two by size shape and the genetic composition it means that what pair number one determines is not the same thing what pair number two determines for example you'll find out that chromosome number 23 pair number 23 will determine the sex you cannot find this in other chromosomes so they vary in shape size and the genetic composition from Pair number one to pair number 22 number one to twenty two are called autosomes what about 20 30 pair is called gonosomes which has x x for female and the X Y for male X you have to know this x is longer and bigger over y why X is longer and bigger over y question why why is X longer and bigger but right doctor will answer that but on the purpose of this um X carries more genes compared to why compare it to y a so so so a care you type an example looks like this you see that chromosome number pair number one number two number three number four they they vary in appearance shape and also they vary in the genetic composition so from 1 up to 22 we call them all this we call them bonosomes we call them aerosomes and then the 22nd pair we call it gonna zones so basically uh does it uh the vision of the process of mitosis it's not it's advisable before you start meiosis to do a revision concerning about concerning about the process of mitosis so guys our next video as we say that we're gonna be having uh prizes air time uh meals yes we send you a vulture and then you buy whatever you want to buy it can be a school bag t-shirts we have a lot of gifts to give out on our YouTube channel so please don't forget to subscribe don't forget to subscribe like share so that others also benefit from this content and then we're gonna be having all the subjects so we are trying to increase this so mitosis occurs in every living organisms in the somatic cell to produce those are the body cells other cells other than sperm and obam to produce genetically identical cells so you can have a hole on the mouse on on the cheek and then uh you need meat so what they can do they can cut the bum and then they put on the mouse you move with the bum or or or on your face basically why why do they do they do that because these cells they undergo what's called mitosis they are genetically identical they are genetically identical they meet from your bums is exactly the same as the meat from your face in terms of the genetic composition so two identical cells are reproduced two identical cells are produced with a identical chromosome number equal to the original cell it means that the parent and the babies or the daughter cells they're exactly the same there is no difference that's why when you get your wound another meat develops those cells which develop the exactly the same mitosis has only one cell cycle I it doesn't have that that mitosis one and a mitosis two no it only has one cell cycle only one silver cycle it means that meiosis when on on the side of meiosis it has two cell cycles meaning that it has meiosis one and also has meiosis two so guys let's look at the process of meiosis yeah the process of meiosis was a very good introduction of of meiosis now let's look at meiosis in detail and this will be our next topic tomorrow don't miss it don't forget to subscribe like and then share the video we will be having gifts uh prizes in the our next videos starting from meiosis thank you very much and also don't forget to like subscribe and share our new YouTube channel in the link below called the bright doctor inside [Music] the lesson thank you [Music] [Music] [Music] please use the link below to get the notes questions and other videos don't forget to subscribe like and share to others for our daily new videos yeah welcome back guys welcome back we are today we are going to be looking at what you call the process of meiosis so we saw the introduction of meiosis and today we will be looking at the detailed process of meiosis and where are most questions come from in examination yeah don't forget that we say that in this video we'll be having some some gifts some gifts for those people who are watching the process of masks don't forget that we say that meiosis is a process whereby one cell divide to form four the other cells these cells are genetically different from each other and from the parent the process of meiosis we say that a type of cell division that results in four dollar cells each cell with half the chromosome number to the parent so message is a continuous process it's a continuous process but it's divided into different phases uh and and and events so the events um for example the first event is what you call the interface interface is a is not part of meiosis you um you must know that interface is not part of meiosis it's just a growth phase because meiosis is regarded as a reproductive uh process in the uh reproductive cells which are determining the the cells which you call the gametes so um it includes a DNA replication that's where where DNA replication takes place remember when you're talking about DNA we asked a question where does it occur we said in the nucleus when does it occur occurs before the cell divides or it occurs during interface So when you say before the cell divides it means that uh interface is not regarded as a phase of meiosis it's just a growth phase it's like saying that you give us a baby and then a baby immediately cannot give birth to another baby need some time for this baby to grow so that now uh once the baby grows then is ready to reproduce when the cell divides and then goes to the last phase it does not divide immediately no it requires some time for it to grow so during that process of growth is what we call interface and the things which occur in that phase some of them is DNA replication doubling of the DNA chromosomes which are single surrounded they become double we saw it that we have what we call the unreplicated chromosomes when they double they become the replicated chromosomes so when the the chromosome has one thread then we call it uh and a replicated chromosome or what you call single standard chromosome but when it becomes a double as we said as you see it here it becomes what it it is called uh replicated chromosomes or double stranded chromosome so each chromosome will consist of two chromatids joined together by a centromere so a chromosome it must have a chromatid it must have a centromere joining it if it is replicated the chromosome it will have two chromatids and these chromatids must be joined together by a central ner centromere is the middle part of the chromosome then um DNA replication what happens in DNA replication DNA replication helps to double the genetic material to double the chromosome number as I said that we don't set increase the chromosome number as we ask a question it increases the chromosome number from what to what so we need to say that it doubles the chromosome number of genetic material so the material so that genetic material so that it can be shared equally by the new cells arising from the cell division it means that now these cells the new cells which are going to be formed they're going to have the content they're going to have the content they're going to have the chromosomes they're going to have other cell organelles equally shared equally because each cell must have these content so if it doesn't have then it means that it will be empty and then it won't be able to survive so it is the function of interface the growth phase uh to bring about the doubling of these organelles and the doubling of the genetic material so that each cell each new cell has a equal amount of the genetic material and also the cell organelles if we have said that our interface is not the part of meiosis then what are the phases of meiosis number one we have what called the prophase number two we have what we call the metaphase number three and what's called the anaphase number four we have what the telophase and then we go to Professor to prophase metaphase two anaphase two Terra phase two so we are talking about uh prophase metaphase anaphase what is it what does it mean prophase means preparation Pro means preparation P versus P then you have metaphase versus middle m versus m and then anaphase versus apart a versus a and then t means still phase T versus D so even in prophase two the metaphase two anaphase two and enter of phase two so we form a if you take the first letter we form what's called ipmat This is in different color it means that this in interface is not part of meiosis that's why we don't have interface one and interface two we only have interface so it means that it's not a part of meiosis so the the the the process of meiosis begin with prophase metaphase anaphase and therapies whereby we say that this is a preparation middle apart and then they have reached the what's the terminal what are those things which we are talking a middle apart terminal what are they we are talking about with the chromosome as you see them here so this is trying to show you exactly uh what is happening so it means that you start with one cell the one cell divide from two cells and then these two cells divide from four cells but actually what is really happening for this cell to divide is what you're going to look at in the details of each phase let's look at meiosis one meiosis is divided into two phases into two divisions not phases the first magic Division and the second magnitude division so in the first metric division it will have prophase one metaphase one another phase one two phase one and then the second metric division we will have uh profits to metaphase to another phase two and then telophase two so the market the first meiosis uh this is called a reduction division whereby when we talk about reduction division you start with 46 chromosome at the end of mass is one you end up with the 23 chromosomes 23 chromosome in each cell hence we call it a reduction division this division results in the reduction of the number of chromosomes from 46 um to 23 in each cell so uh the resultant gametes are haploid it means that they have one set of chromosomes from chromosome number one to chromosome number 23 they are not paired it means that they are single haploid half it means that the cell has 23 chromosomes you know it's 23 pairs of chromosome all right let's look at the phases of of of meiosis the first phase is prophase which means preparation the cell is preparing for whatever is going to be uh doing so the first thing is chromatin Network we say that chromatin Network means that uh entangled entangled DNA DNA is in form we don't have a direction when we look at it we don't know where it starts or we don't know where it ends so it is chromatic Network when it condenses it forms it becomes thick when it becomes thick it forms what's called a chromosome so the chromatic Network contents when they condense it means that now that it has formed the chromosome now these chromosomes the chromosomes which look alike homo which means the same logos which means structure so it means that chromosomes which look alike chromosomes which look alike they are going to come together that's why you're saying that homologous chromosomes are formed it means that the chromosomes should look alike they come together when these homologous chromosomes the way you see it here when they they they they they they they they come together they cross over what do they use to cross they cross using the chromatids the one chromatid of one homologous chromosome crosses with another chromatism of another chromologous chromosome and then the process continue so the spindles already starts to form it means that now the spindle fiber they start to form and then once they start from the nuclear membrane starts to disappear let's look at the diagram here so you see that here the the the the the chromosome they condense the homologous chromosome you see this one is short this one is long so this shot cannot go with the long one no the shot goes as well the shot the long one goes the the long one that's the principle this these chromosomes they come together and then the chromatids they cross each other when they close each other we call it crossing over that's why we're saying that crossing over takes place and then the point where they cross over we call it chasma we're going to look at this in detail and then now this window they start uh the same rules they start to move to opposite poles as they move yes as they move they spindle is 32 form so once you see something like this they have crossed like this then you just know that yes this is is profits why because the chromosomes are crossing over homologous chromosomes are crossing over we don't have crossing over anywhere else except in prophase one no even not in prophase two we only have it in Phase One why in phase one because the chromosomes are still in homologous pairs let's look at the process of crossing over so we have seen that the homologous chromosome the chromosomes which look alike they're going to align together when they align together one chromatid of each chromosome overlap so it means that they cross each other when they overlap these chromatids they must be overlapped based on the homologous pattern for example it means that the one chromat is from one homologous chromosome and another chromatid form another homologous chromosome they cross over and then when they overlap and they cross over it means that they cross over at a point called chasma and then crossover takes place at a point called chasma if this one with chasma if there are many you call them just matter so when we say chasma or chasma burning on the kind of English you are using then um chasma or chasma is is is is is one is a point where these two homologous chromatids cross over during prophase one and then now the chromosomes separate so it means that now they have formally different chromosomes I always ask this question to to different people are you sure your father is your father why am I asking you that you don't resemble him actually you don't even resemble your mother you walk you go somewhere and then you find out that you resemble someone why and they ask you that hey when are you resemble someone I I know that why basically he might be your father but because of crossing over this made to the exchange of the genetic material if you came from the same father same mother you breastfeed on the same breast of your mother why don't you look alike it means that this crossing over this process of meiosis helps in bringing about variation among organisms so it is a very important process to make humans individuals different from each other and then this helps in the survival if all of us we are the same then it means that we won't be able to survive imagine everyone is rich do you think that there will be someone who is working for another one everyone has money you think I would have taught you this no because I don't need you don't need this no one would have been watching you don't need this you have your money what else you want but because there is difference among these organisms among us then it brings about what called competition hence different people will work differently and in different environmental conditions so that's the purpose of meiosis to bring about variation among organisms of the same species all right let's look at continuing with the process of crossing over so these differences is being brought about by crossing over imagine a father producing uh over 100 million sperm for a single age actuation and then this sperm each sperm is different from each other what made them to be different from each other is the process of crossing over because it forms different combination of chromosomes all right let's look at so we think that you have one homologous chromosome and another homologous chromosome they come together yes when they come together they overlap the chroma homologous chromatic overlap at a point called chasma yes if you look at ABC and then inside ABC yes when they cross now this one takes this red and then the red takes the blue that's why you see it here the blue takes the red and then the red will take the what the blue this chromosomes during crossing over scientifically we call it a bivalent or bivalent based on how do you write that how do you pronounce that bivalent or be valid and then after that they separate so that each chromosome has genetically different uh each chromosome has different uh material from uh one another look if you see that ABC starting with a b c but this is a small error the small era was found on this chromosome and this is one ABC but this one is a capital letter the capital letter came from this Brew if you look at it here it came from the blue it means that the blue they already took the blue and then the blue took the what the red so because of this it's gonna cause different uh gametes being formed and then if you look at it sometimes we can bring it in the exam like this uh homologous chromosomes when they cross they close from top so when it crosses from Top it means that you have to draw it on top don't grow it down that's one of ways of of losing max if you don't show the variation correctly so you have the chromatids crossover and then the exaggerating material or the information and then now the chroma chromosomes now have new combination of the genes guys don't forget that I told you that there is a gift uh in this video just click that link below it will take you to a specific page on our website and on that page there is a code for you to obtain that airtime enjoy it when you get it when you load it on your phone let us know that you got it thank you very much let's continue and then you're saying that the second phase is metaphase one metaphase one meta means middle it means that now the chromosomes are always in homologous pair homologous chromosomes randomly align along the Equator along the Equator of the cell in plurals it means that they they align along the Equator in two rows one um from chromosome chromosome number one chromosome number 23 another one is from chromosome number one to chromosome number 23 that's what it means each chromosome is attached to the spindle uh the spindle uh thread from each pole this is what I'm trying to say so they align in two rows you see this is the Align in pros and then these chromosomes are being held by the spindle see each chromosome is attached uh uh to the spindle threat from each other they do this they do this Arrangement randomly so the key point is homologous because they're in pair and then each other you see this one cannot come here no they must be together like this homologous chromosomes yes that's a key point and then they they come here randomly remember we have print repairs but we're just showing you two pairs yes they are here randomly it means that another one can be this one can be on top so this set can be on top this one can be down or this chromosome can be this side this one can be decide that's what you call randomly so when they separate we're gonna form different cells so each chromosome is attached to the spindle fiber or spinocerated from each part that's what we are trying to show you that this threads are attaching the what the chromosomes from each pole so after that once they are done with this then they start to move apart which you call anaphase so in anaphase the spindle thread is shortened they try to pull when they shorten they pull it's like when you your body builder when you carry something the muscle is shortened when they shorten they pull yes so they pull uh the homologous chromosome to opposite poles and then the chromosomes what happens to the this chromosome the homologous chromosome pair then they do what they they separate the chromosome of the chromosomes of the homologous pair they separate it means that now they move to opposite poles this is what is happening so now they move to opposite poles and then now uh when they move to opposite poles now they reach the pole so in telophase each chromosome or chromosome reach at the poor of the cell and then once they reach the power of the cell the cytoplasm and the cell membrane divide when the cytoplasm and cell membrane divide that process is called cytokinesis we call it cytokinesis the vision of the cytoplasm and then the two haploid cells are formed to haploid cells are what are formally and then the nucleus the nucleus or the nucleolus that dense body in the nucleus they reform then it reforms and then lastly the new nuclear membrane forms and then now they cell appears to be a full cell so this is uh what I'm trying to say yeah so now you have a form of two cells now these cells cytokinesis took place and now this is the nuclear membranes that will reappear and then the cell goes back as if it is in profits so now when it reaches there now now each cell each of it it will undergo meiosis too it means that now this one is going to go under meiosis two even this one is going to go undergo my system so that you form two here and two here so when you add them you form four cells so when you go to meiosis II what happens now prophase two you go to prophase two when it's meiosis two profess it becomes prophets to 18 months the two must be there if you don't write it there we won't give a mark because we don't know which prophase is it so prophase two what happens the nucleolus remember we said that it it appeared they reappeared so now the nucleolus and the nuclear membrane they disappear again but now here we don't have crossing over so the new uh spindle fibers are formed yes they start to form and then the chromosome become visible it means that they condense and then it becomes visible and then now once they become visible now it's ready to undergo metaphase they go to the middle of the chromosome uh the cell so now you see it here now it is forming like this and then now they are ready to move this this thing to attach themselves to the chromosome but now we don't have homologous chromosomes we have chromosomes which are not homologous it means that crossing over cannot take place because it already took place before before yes so now uh in the metaphase two the individual chromosome line up here individual or one chromosome aligned along the Equator singly or individually so the other side we say that chromosomes align along the Equator in homologous pair and they randomly here they align along the Equator singly or individually so you have to know the difference so sometimes you ask you the difference one animals is two you can use the process to differentiate between the two so at the equator of the cell with the centromere attaching the spindle fiber or Central May attached to the spindle fiber and then now uh this is the picture if you rotate it you will see that these chromosomes are in the middle you see the in the middle if this is the pole and this is another pole they're in the middle so this one becomes the equator remember I say that equator is an imaginal line it's an imagined line it's a line which we just imagine but the line is only there is a marginal line which divide the cell into two equal parts the same thing equator of the earth marginal Line running from east to west and dividing the earth into two equal parts we're just imagining but the line in actual sense is not there we just imagine that that's the center of the Earth so we just imagine that's the center of the cell so in anaphase once they're in the middle they now they have to separate to opposite poles so in anaphase two you have spindle fibers start to form so the spin of fibers they contract when they contract it means that now they pull the chromosomes apart but now because they are single chromosomes they are non-homologous now is this the the the the the the chromatids which are going to separate remember chromosome is divided into two chromatids now one chromat is gonna go one side and another chromatid is gonna go to another side of the cell so this is what I'm saying that now the chromatids move to opposite it was together here now this one pulls it inside and this one pulls this side check the direction of the it's not facing this way it's facing that way because the force of pulling is coming from the side so that's why it's supposed to be like that when you're drawing make sure that you are you take caution when you're drawing it so that you draw it properly and it's checked about the shadings also the shadings are very important when you are doing it the Dora chromosomes reach the poles once in in telophase II in telophase 2 the dollar chromosomes reach the poles when they reach the poles we don't call them chromatids anymore we call them chromosomes actually that's what we call single stranded chromosomes or any replicated chromosomes so it's supposed to get time so that this time allows these chromosomes to grow so that now it becomes double stranded again that's why we need what you call interface so new nucleus uh then forms it means that the nucleolus also come back what it means that it reforms then the cell membrane of this of each cell constrict and then the process of cytokinesis occurs when the cytoplasm divides now the process of cytokinesis occurs and then four haploid it must be haploid there are cells are formed and then now each daughter still have have they have the chromosome number to that of the parent so that's why you're saying that meiosis is the process whereby one cell divide to form uh four dollar cells which are haploid or which have half the chromosome number to that of the parent and these chromosomes are genetically different because of the crossing over which took place so the daughter cells are genetically different as I've just said and then these are the cells which will form from four other cells and then you you see you don't call these ones chromatids we call them single surrounded chromosomes watch out to this before you write your SBA so the importance of masses what are some of the importance of meiosis let's look at the importance of meiosis just start from there with the importance of of meiosis anxiety is giving me a lesson thank you very much [Music] please use the link below to get the notes questions and other videos don't forget to subscribe like and share to others for our daily new videos So today we're going to look at the importance of meiosis non-disjunction how does non-disjunction bring about Down syndrome and then we wrap up with this topic and then we can start the topic of reproduction in vertebrates so that the other time you come back we can start a reproduction in human or what you call human reproduction all right importance of meiosis before we start the importance of myosis don't forget that meiosis is the process whereby one cell divide to form four dollar cells and each cell has half the chromosome number to the parent it means that the cells which are being formed under meiosis are different so and then we we say that meiosis results in haploidy cells and these cells are specifically for gametes based on that information we can identify some of the importance of meiosis so what are some of the importance of meiosis the first one is the production of haploid gametes we'll talk about the gametes we say that gametes these are sperms and over so these sperms are haploid which means that if they are diploid if the badasserole is deployed it has 46 chromosomes now the gametes they're going to have 23 chromosomes if it is a human cell so number two is having effect of the meiosis overcomes the doubling effect how is this having effect being brought about when you talk about having effect remember uh remember that that we we started with the uh you start with uh 46 chromosome this 46 chromosome they divide and when they divide you form uh one cell another cell and then this one also divided from another cell another cell we want to explain the effect this issue of having effect now this is 23 this is 23 this is 23 this is 23. so now it means that the sperms or over which are being formed here they're going to be uh they're going to be 23. now if you bring about um if you bring about for example a sperm uh fuses or fertilizes the ovum the ovum and then this arguments remember the engineer this is 23 and also this is 2 and 3. so now when they fuse during the process of fertilization now you go back to 46. so it means that this is Fusion this is fertilization so this is the doubling effect this and this they double to form 46 but now meiosis is going to divide them now to form 23 23 that's why here they are saying that the halfing effect this having effect this having effect is being outcomed by it by the what the doubling effect of fertilization so this is fertilization while this is meiosis so it means that this helps us to keep the the number of chromosomes in one generation to the Next Generation constantly but if this having effect was not there the mean is that if fertilization occur us now it would have been Now 46 46 and then you form another one which is 92 then 92 again 90 to 92 again you you form a big number so this halfing effect this um doubling effect is being out uh come by doubling effect the having effect out um overcomes the doubling effect of fertilization so meiosis results in reducing the chromosome number so we're saying that thus maintaining the constant number of chromosomes uh from one generation to the next T generation so now uh we are saying that um this produces number two another thing is um it produces what you call the genetic variation remember in in in any prophase one remember in prophase Pro uh phase prophase one you have a process called the crossing crossing over this crossing over it helps in in exchange of genetic materials so because there is exchange of genetic material then you will have different sperms uh we know that you produce over 300 million sperms for a per a single generation so each pump is different it's as a result of rough phases during the prophase uh in the process called crossing over so it brings about new recombinants new combination of genetic material um we are different from our sisters and brothers is because of basically uh because of the process of crossing over why is meiosis important for survival do we need uh reduce meiosis for survival or do organisms which don't under meiosis survive we need to this mouse is so that we can create differences among individuals of the same species if these organisms are known at the same then automatically it means that there won't be differences imagine I I ask you a question last time that if everyone is Rich what will happen if there is there are no differences among us if everyone is clever you don't need to read everyone has the information it means that there will be no competition so the reason why mercies is there to bring about the differences among organisms of the same species you can survive in hot environment you can survive in in cold environment you can survive and add-ons who survives in hot environment can't survive in in cold environment so it brings about that now all the the environment can be occupied by different kinds of people yes if you can't survive then it means that you have to migrate to the the area which you can survive or where you can compete better if you can't then you you die you you are wiped out so the importance of meiosis is to bring about um variation so that now there is there is there is a survival of these organisms in the population so it is a great importance because it creates genetic diversity in the population hence difference in the survival of the organisms in the environment so basically that's what I say that it brings about what called survival from there let's look at uh what you call the the non-disjunction the consequences not disjunction and the consequences when you talk about non-disjunction you need to know where does it occur which phase we need to know the phase the phase where does non-disjunction occur so it occurs in in anaphase it can be anaphase one or it can be anaphase two and then what is the importance of this non-disjunction oh there's non-disjunction has any importance or it has the negative effect on organisms so that is what you're supposed to cover in the so we are saying that non-disjunction each nucleus should contain 23 chromosomes you have to know that if it is a human cell this is a human cell that each nucleus must contain 23 chromosomes after meiosis but if now are non-disjunction occurs the means that uh if the chromosomes fail fail to separate to separate if uh chromosomes fail to separate that's what you call the non-disjunction and during anaphase if the chromosomes fail to separate then it means that this number of 23 will not be brought about so one nucleus so now what happens in non-disjunction yes okay saying that you have a cell a sale under metaphase Mera Mera phase metaphase one and then now this cell has uh chromosomes remember they are supposed to be aligned along the Equator you see we're explaining the process of non-disjunction they're supposed to be aligned along the Equator now in actual sense in the normal cell if it is normal yes we expect it to be like in anaphase in anaphase in an office I expect it to have these chromosomes separating these chromosomes separating you see these chromosomes must separate you see they are separating and then in telophase I expect this cell to form two cells from two cells whereby these two cells they have two chromosomes you understand so if it is a normal cell I expect it to be 46 um now this one is also 46 after at the end of uh tell phase one telophase telophase one I expect to be 23 and even so this one 23 but if non-disjunction occurs if non-disjunction uh disjunction occurs what happens metaphase the chromosomes yes they will be fine like that in metaphase they will do what they will be fine yes and then when they go to anaphase now we because we said it fails to separate during anaphase yes this one is a 46 if it's a human cell then automatically it's gonna be now what's gonna happen is gonna happen that the whole set the whole this this whole set is gonna go to one side the spindle fiber are going to fail to to contract from this other side you understand and then it pulls this one also pulls this one but this one is going to go on one side you see it's gonna go on to one side now this is going to result in a Cell having yes one two and then three one two and then three and then the other one is gonna have only one chromosome you understand so now it means that this one is going to have an extra extra chromosome this one is going to have an extra extra chromosome yes and then this one is going to have short is going to be less of one one chromosome so it's gonna have an extra chromosome this one's gonna be less of one chromosome so now if this one is still 46 now this one is supposed to be 23 but it has an extra therefore is going to be 24 and then this one is supposed to be 23 but now it has is short of one chromosome it's supposed to have two chromosomes now it has three it has one extra and then this one is supposed to have two but now it is having one it means that is short of one chromosome if we go back to a human cell it's supposed to be 23 then it means that it's going to have 22. so now what happens so because now uh it has an X it has three three chromosomes then in science we're gonna call it price of try try we call it Zone because it is a cell the body which describes a cell which has uh three chromosomes of the same kind uh on the uh three chromosomes of the what of the same of the same kind the name here is gonna be because this one is gonna be mono mono because it's a it's a cell a body then you're gonna call it Zoom so it's gonna call it monosome if this non-disjunction occurs on chromosome number 21. then we're gonna call it uh try Zone price on point one we're gonna call it dry zone 21. now what happens what happens if this cell which has 24 chromosomes the trisome they try Zone 21 price on 21 if it fertilizes a normal gamete for example this is a sperm and then fertilizes a normal gamete which is the ovum yes oven then automatically what you're gonna have is we're gonna have a normal oven remember it has a normal cell is going to have 23. so now it's gonna have uh 24 and 23 then you're gonna have 47. remember a normal person is supposed to have 46. now instead of 46 it's going to have 20 uh for it sorry 47 so it means that now this condition because of an a normal uh cell fertilizing uh the cell which has an extra chromosome on chromosome number 21 is going to result in what you call uh down uh syndrome syndrome is when I result in what you call down syndrome that's how Down syndrome is being brought about however we can also have a situation because we say that uh this cell is having 22 instead of 0.3 so now if um if 22 if 22 fertilizes the one which is 23 yes now it means that it's going to have 45 instead of 46. still this is also an abnormal uh individual so a monosome if it fertilizes um a normal cell is going to become 45 and then a trisom it fertilizes the normal Cell It's Gonna form 47 all these results in abnormality in an individual so uh that's what we are trying to explain so now when we say that um one nucleus of uh wind dance the afternoon disjunction occurs as we say that one nucleus content will contain 22 chromosomes we have seen where do we get the 22 chromosome it fails to separate and then uh one nucleus is going to have a 22 chromosomes of instead of 23 while the other ones will have 24 instead of 23 it means that this one is the monosome and then this is a trisomer it is less of one chromosome it has an extra of chromosome when either of this resulting gamete fuses with the normal gamete normal gamete is 23 so now if um uh this fertilizes this uh 24 and 23 is going to be 47 22 and 23 is going to be 20 45 that's why they're saying that result in 45 or 47 chromosome instead of 46 which is 23 plus 22 you get 45 we have explained that and the 20 three and 24 you get 47 instead of what 46 23 plus 23 so this is this will lead to a child having what you call Down syndrome Down syndrome and then the child will have for his uh five autosomes with three uh chromosome number 21 it means that chromosome number 21 is gonna be three of them that's why we call it trisom that cell is for the try Zone because they have three chromosome number of the same kind instead of a normal pair and one pair of six chromosomes so six chromosome so if they're 25 plus the six chromosome which is X and Y or x and x based on which gender is it then it's going to become 47. and then the women over the age of 40 and have a great chance of having children with their own syndrome we're not saying that uh children uh all the people who are four years and above they're gonna produce kids who are having Down syndrome complications you know we are saying that the people who are four years and above they have a great chance of having this imitation have a great chance of having a baby with Down Syndrome I think you have ever seen people with a Down syndrome you have ever seen them so what are some of the the the the the the characteristics of people having Down syndrome Story the body is talking uh flattened face with small and broaden all small skin oh yeah you you you have ever seen these people uh let's look at a picture which has Fall Down syndrome here so uh the falls in the inner corner of the eyes that appear to be slanted upwards and then um a large tongue these kids they have large tongue actually the tongue is always protruding out yes with the small eyes actually the eyes are tilted yes and then you're saying that they brought the hands the hands are big and short they're actually fingers they're big and short they're broad big and short and then you're saying that uh wide space between the first and the second tall if you check the you may not see the the the the the kid because of the shoes all right but if you get a chance uh this kid to remove the shoes you can see exactly what is happening yes so now let's look at some of the differences one analysis to here we say that we explain this that if you wanna know what the differences between meiosis one and Ms is two just look at the phases prophase what happens in prophase there is no crossing over there is crossing over there is in in my metaphase uh chromosomes align along the Equator randomly in homologous pair chromosome line along the Equator singly so and then anaphase chroma homologous chromosome separate to opposite poles where the other one chromatid is separate therapies you form two chromosomes sorry two cells the other ones you form four cells crossing over occurs in profits there is no crossing over so you have to look at the phases okay chromosome align along the Equator in homologous pair you see the word homologous in the homologous this is the key point in the homologous pair then the other side the chromosomes align along the Equator individually this is the key point to which which which which um differentiated them then they are saying that the chromosomes move to opposite poles they move to opposite poles they are not saying they're saying chromosomes it means that uh the way a chromatids now sorry homologous chromosomes so the chromosomes now they move the opposite part what moves to opposite poles in terms of uh meiosis too is there chromatids chromatids uh move to opposite to opposite poles yeah why do we call them data chromosomes they have not yet developed to form real chromosomes that's why we call them the other chromosomes but we prefer saying chromatids two cells from uh two cells form at the end so we say that here you form two cells where the other side you form four cells you see the key Point yes and then our chromosomes number in in meiosis one is halved chromosome you have the halfing here you have the halfing event you can't see because of the color and they decide uh the chromosome number is maintained it means that you start with 23 and then you end up with 23 yes then uh crossing over takes place we say that there is crossing over while the other side there is no crossing over there is no crossing over basically those are some of the differences between meiosis what about the similarities do they have uh do we have some small businesses and mitosis yes obvious there are some uh similarities what are some of these methods both process involves division in meiosis one you have what's called a cytokinesis even in mitosis you have what's called cyto cyto cyto Kinesis division of a division of the nucleus so both cells you have uh new you have cell division it means that new cells are formed however in meiosis you form four cells and then in mitosis you form two cells which are identical both process occurs in M phase M phase is a phase whereby the the cell starts to divide the the cycle is divided is divided into M phase you have uh the the G phase one uh the S phase and then the G phase two this all this is interface interface that's why you call recall that this is not a part of meiosis and I can call this uh growth uh sorry growth says close one synthesis grows two and then this is uh where there is a division the real division which is taking place actually it it takes around 80 minutes minutes for it to to to to to to happen well this one takes around uh the remaining from 24 hours that's how What It Takes yes all right in both cell cycle the stages are common you have metaphase prophecies and telophase both in meiosis and in in in in in uh mitosis the synthesis of DNA both you'll find the symptoms of DNA in interface you see here in the in the S phase which you call synthesis that's where you find the organelles and DNA are being synthesized from cytokinesis division the vision of the of the cyto cytoplasm yes cytokinesis occurs in the two cells what about the differences between mitosis and meiosis difference between mitosis and meiosis okay uh here we see that it occurs is in the celebrity uh what you call the somatic cells well this one occurs in ovaries and testis resulting in gametes production of genetical identity these ones are identical The Identical word this one is genetically different they are genetically different this one results in two DOTA cells uh while this one results in four other cells these cells must undergo maturation interface so that they can mature so that they reform what you call real cells you've got them daughter cells because they are still young then you have one nuclear division you don't have mitosis one and mitosis two no so it means that the nucleus device once that's why we say one Nuclear One nuclear well here we have two nuclear division uh here we have uh crossing over takes place in prophase one while here crossing over takes place there's no uh there is no crossing over in in prophase one that's why they're always identical well in meiosis there is crossing over which takes place in prophase one then here we said that it results in dollar cells being deployed you started with the diploid you start with the deployed to end you end with deployed to end while here I start with the deployed to end and then you end with a haploid one end you see yes then here results in the somatic cells where this one results in the gametes so basically uh those are the differences between meiosis and mitosis so now let's look at so I think our next class lets it to be a reproduction reproduction you're going to look at the reproduction I know that many people like this topic and then even in my uh sorry Even in our new YouTube channel for bright doctor we're gonna also discussing too much of reproduction yes check the link below don't forget to subscribe and like and also share to others so that they can also benefit from our our classes thank you very much see you again foreign [Music] please use the link below to get the notes questions and other videos don't forget to subscribe like and share to others for our daily new videos yeah well others for our daily new videos yeah welcome back guys welcome back to our class we are looking for distinctions and making sure that we pass all of us we must pass we must go to the university yeah I've got the vote Yes today we are going to be looking at what you call um meiosis I know meiosis is one of the difficult topics very simple to take to grasp but try to answer your questions let's look at meiosis meiosis we said that meiosis human reproduce what other organisms they reproduce they multiply what about cells cells they have two kinds of reproduction they undergo they have multiple mitosis and you have what you call meiosis my my process can occur in other body cells but meiosis occurs only in the reproductive cells where did you come from actually meiosis was the basis of you living without meiosis you then have existed so let's look at meiosis in detail so it's a type of cell division that results in four data cells each with half number of chromosomes through that of the parent so it means that meiosis starts with the uh it starts with the one cell this cell divides and then you form four Dora cells these cells they have half the chromosome number to that of a parent if you have started with the four chromosomes it means that uh the these cells will result in two chromosomes that's why you're saying that half the chromosome number of that of the parent if the man yeah the body cell is having 46 chromosomes then the the reproductive cells or the daughter cells which are resulting from that are going to be having 23 and then from the mother also 46 they're going to result into 2.3 so the process of reducing these cells into have the chromosome number that process or that reproductive process is what you call meiosis so what does meiosis result in so this message will result in the production of gametes gametes these are the sperms and the over and talk when you're talking about the humans and then plants you're talking about spores in the pollen grains you can talk about the obvious those are some of the things uh which as a result of of meiosis so in humans or in animals it occurs in the ovary you see this colored word in the ovary uh basically uh over a phone in a female and then these ovary they produce what you call the over so the reproductive cells in the film in the females call them over if this one is called the other if there are many you call them over and then uh in in male in male because it is occurring in testis and then and testis uh what we call we call them spermatozoa the cells which are being produced you call them spermatozoa so in female we call them ovary those are the over raised ovaries produced over and then in in testis uh they produce what's called a spermatozo what about in plants in Plants occurs in the ovary still but what it produces over reproduce What's called the obvious meiosis occurs in the anthers and then what it is being produced is What's called the Polynesian so the question can come and say that um other than the ovary in animals which other place does uh meiosis occur that is testis and what does it produce it produces what we call the spermatozoa and then in in in plants uh it occurs in the ovary it produces what you call the obvious basically uh that's what you need to know about this first introduction of of meiosis you know meiosis is basically the cell divides and the most important thing to divide is the nucleus so so we need to know the nucleus to do a recall about the nucleus because we saw the nucleus at the beginning of DNA and also saw the nucleus in the grade 10. so let's look at the nucleus the centrosome and then the cytoplasm nucleus contain the genetic material what about inocytominus uh cell and then plus means a fluid the fluid of the cell so basically this is what you are going to look at let's look at them in detail so this is a cell it has a nucleus outside you have what's called a cytoplasm then in the cytoplasm you have what called the centrosome centrosome why do we talk about the nuclear centrosom and discipline because uh uh this uh the DNA you'll find it there and then it is the centrosome which which produces the centrioles and the centrioles spindle fibers which hold the chromosomes in position that's why I talk about it and then there is a time when this one disappears and then you remain the content of the cytoplasm so the nucleus disappear and then remain only with the content of the cytoplasm so basically that is a nucleus and then when it brings it in exam it looks like this so this is a nucleus as a nucleus but the nucleus has a density body which we call the nucleolus nucleolus then outside the nucleus if you have the nuclear membrane which has the extensions extension which you call the endoplasmic reticulum but because it has the ribosome they look rough then we call them the rough endoplasmic reticulum the rough endoplasmic reticulum so basically uh that's it it has the nuclear power the holes where substances go through most especially messenger RNA in this case and other substances then it has what you call the nucleoplasm the nuclear the plasma of the nucleus meaning that the fluid of the nucleus the nuclear envelope that's what you call the nuclear membrane then the ribosome we say that the ribosome decides for protein synthesis chromatin this one is done which condenses to form chromosomes and then you have the nucleolus so we have explained all that so when you look at the nucleus or when you look at the DNA basically that's what you see you have when the chromatin Network condensed you from what you call the chromosome so the chromosomes they condense you see they have condensed and then after that you form a real structure of your chromosome it looks like this so that's the structure of a chromosome now let's look at the chromosome in detail so we have seen where the chromosome come from it cannot exist without DNA with this specific genes you see it has specific genes so let's look at the structure of a chromosome why do we need to look at chromosome will you resemble your father because of the chromosome because of the genes you obtained from your parents your father your mother what about those who don't resemble the father and the mother but they resemble their grannies we shall see another question what about why so in this topic we're gonna see why why do you resemble uh your neighbor why do you resemble when you go somewhere when you go somewhere someone can say that hey we're not you resemble someone why do you resemble someone those are some of the questions we are going to answer and this is the reason why we need the structure of the chromosome so the structure of the chromosome chromosomes as thread-like structures present in the nucleus the thread-like the thread-like it means that they are like strings centralized structures found in the nucleus that's why we talked about in your