hey guys it's medicosusperfectionellis where medicine makes perfect sense we continue our biology mcat playlist in the previous video we have discussed mitosis today it's time to talk about meiosis which is important to make gametes for your ovaries or your testicles as you know cell cycle consists of the interphase and the m phase mitosis or meiosis take place in the m phase g1 is for growth s is for synthesis which means dna replication g2 is another growth and then you go to mitosis or meiosis if you remember my last video i've told you that in mitosis each parent cell will give you two identical daughter cells and if the parent cell was 2n which means deployed the two new daughter cells will also be 2n however in meiosis when the parent cell is 2n it will give you 4 cells mitosis versus meiosis what a clean comparison mitosis happens in somatic cells but meiosis sex cells gametes your ovaries and your testicles mitosis is not involved in sexual reproduction but moses of course is involved in sexual reproduction mitosis will give you two diploid cells meiosis will give you four haploid cells mitosis has just one round of division just one cycle but meiosis has two rounds of division the first one will give you two haploid cells and then during the second round of division they will give you four haploid cells and that's why we call the first round of division reduction division because we have reduced the cell from 2n into n however in the second round of division it's called the equatorial division why is this because it's equal to the parent cell here is haploid and haploid if you remember mitosis had four phases prophase metaphase anaphase and telophase however meiosis has two rounds of division so how do you differentiate between the two rounds you call the first round prophase one metaphase one anaphase one till phase one and then you call the second round prophase two metaphase two anaphase two and telophase two what does pro mean before it's before all the other steps it's also before the metaphase meta meta means change what do you mean by change alignment you can also say meta in the middle because everything is aligned in the middle of the cell in the equatorial metaphase plate next you have the anaphase and amines up which means separation you separate the two sets two opposite poles of the cell and then the till phase telos means purpose the end yeah the end and h1 making its own nuclear membrane and now we have separate daughter cells if you'd like to learn more about mitosis please watch my previous video in prophase of mitosis you had condensation separation formation dissolution then you have metaphase meta alignment meta in the middle everything is aligned in the middle in the equatorial plate mitosis anaphase ana away ana up separation separate me split each centromere into two separation of the sister chromatids and then the kinetochore fibers will shorten pulling the sister chromatids to opposite poles of the cell mitosis telophase telos the purpose the end which is the opposite of the prophase at the beginning in telophase you have disappearance of the mitotic spindle formation of a nuclear membrane formation of cleavage furs and uncoiling decondensation of the chromosomes the parent was deployed and each daughter will be deployed because this is mitosis however in meiosis the parent was deployed but the daughter will be haploid that was the story of mitosis in a nutshell remember just one round of division however in meiosis you have two rounds of division here's the first round here's the second round everything in the first round is called one profis one metaphase one and a phase one telephase one and then each one of the daughter cells will go to round two and then you have prophase two metaphase two and a phase two and telephase two prophase one is way different from prophase of mitosis because here in prophase one we have a new phenomenon of crossing over look at this beautiful chromosome and this beautiful chromosome they basically hug each other and they they exchange pieces of the chromatin and then you get new which looks weird this process explains why out of 7.8 billion people no one looks exactly like the other it's thanks to crossing over crossing over also metaphase one is different from metaphase of mitosis if you remember the metaphase of mitosis look at the alignment look each chromosome here has a spindle fiber and a spindle fiber from both sides however look at each one oh only from one side and that's a huge difference ana means away means separation and then telophase the telos the nuclear membrane is starting to form and then you have two daughter cells the parent was deployed but each daughter is haploid and this was the end of round one round two will start for each one of the daughter cells this will go to round two and this will go to another round two let's just take one of them you go to prophase two metaphase two and a phase two telophase two basically these are the same as mitosis there is no crossing over each chromosome is connected to two mitotic spindles from both sides etc etc the only difference between meiosis ii and mitosis is what did you begin with in mitosis i started with 2n deployed but in meiosis 2 i started with a haploid and the rest is freaking history so meiosis started with 2n deployed and gave you 4 haploid cells so if the parent cell was 46 chromosomes each one of the total cells will be 23 chromosomes oh but hey mitochosis this was 46 but if we add all of these together they are 92. oh yeah this is the whole point of freaking replication doofus look at meiosis and the end result of meiosis wow if you have noticed meiosis started with a diploid cell and then it gave me four non-identical daughter cells if you actually look at them they do not look the same there are no similarities between any of them and that's why you look different from your sister or your brother and you're different from each one of these 7.8 billion people all of this was thanks to crossing ova which took place during prophase 1. this crossing over is responsible for that genetic diversity and this is the essence of sexual reproduction asexual reproduction however gives you identical offspring identical daughter cells that are similar to each other and similar to the parent cell so tell me more about this beautiful phenomenon of crossing over which is responsible for the genetic variety we start between homologous chromosomes here is a chromosome here's another chromosome and between the homologous chromosomes we cross over at this intersection point called chiasma crossing over can be singular at one side or double at both sides when these chromatids are aligned together look at these four one two three four we call them the tetrad please pay attention the crossing over did not occur between sister chromatids no no no it occurred between homologous chromosomes hey give me something give me something but it did not happen between the sister chromatids because this will not make any difference and this will not cause any genetic diversity it would have been like taking a tire from the front of your car and putting it to the back of your car no difference whatsoever this is not gonna contribute to automobile diversity mitosis end results on the other hand deployed parent deployed daughter deployed or the daughters are identical between themselves and they are also identical to the parent cell now let's talk about meiosis one we're not going to talk about meiosis 2 because meiosis 2 is almost identical to mitosis which was discussed in the previous video tell me about prophase 1 you have the crossing over crossover between what between the sister chromatids oh shut up between homologous chromosomes yielding recombinant chromosomes these are the new creation next you have metaphase one metaphase m for the middle alignment equatorial plate formation at which the tetrads will align notice that each pair attached to a separate a separate spindle fiber unlike mitosis anaphase ana away separation disjunction of homologous pairs not between the sister chromatids the sisters are still together the disjunction the separation occurred between the homologous pairs of chromosomes and this is different from mitosis because in mitosis the sisters got separated the telos formation of nuclear membrane around this one and around this one because we are getting ready to divide into two cells each one of the new two nuclei will contain a haploid half of the number of the genetic material if the parent was 46 the daughter is 23. let me tell you about the phenomenon of disjunction physiologically and pathologically normally it occurs in the anaphase yeah ana means up separation oh separation disjunction and this beautiful separation is responsible for mendel's first law of segregation which means separation of two homologous chromosomes each one ending in either of the daughter cells is a random process in other words let's say that this is cell a and this is cell b cell b cannot say oh i am entitled to this purple chromosome with two orange pieces shut up you are not entitled to anything this is a random process snowflake pathologically when disjunction doesn't happen we call it guess what none disjunction oh look at this instead of separating them into equal pairs oh my goodness here is one and here are three out of the tetrad so instead of giving me two 23 cells now one is 22 one's 24 oops let's imagine that this is an ovum okay get it a normal sperm which is 23. now 23 plus 22 equals 45 a condition known as turner syndrome how about the other abnormal ovum the other abnormal ovum is 24 match it with a normal sperm 23 and now he gets 47 a trisumi a condition known as down syndrome if it's trisomy add chromosome number 21. what if the trisomy happened at chromosome number 18 this is called edward syndrome how about a trisomy at chromosome number 13. this is called patau syndrome most excellent students only know those three trisomies but in fact there are bazillions of these just open the textbook of nelson's pediatric and you'll be shocked it will become clear to you that you are nothing but an enthusiastic ignoramus down syndrome is a non-disjunction affecting that somatic chromosome however this non-disjunction is not peculiar to the somatic chromosomes it can also happen to sex chromosome so this is 47 but it's not trisomy 21 no it did not happen in the somatic chromosomes that happened in the sex chromosome is 47 and it's actually 44 plus x x y normal males are 44 plus x y but this is 45 plus x x y which totals 47 and this is client filter syndrome some pearls for the pros now you know the difference between disjunction and non-disjunction disjunction should happen in the anaphase disjunction is responsible for mendel's first law of segregation there is another concept called gene unlinking and centimorgans basically you look at the genes genes that happen to be close together tend to be inherited together so imagine if you have a gene right here and a gene right here during crossing over since crossing over involved the other sister okay they stayed at the same location together i'm with you forever let's imagine that the two genes were on the other sister that was involved in crossing over they will cross over from here to here together i'm with you forever okay middle coast is cool but why do i care because we can use this phenomenon to measure the distance between genes on the chromosome and the measuring unit is called centimorgan it's like centimeter gregory mendel's second law of independent assortment is thanks to the phenomenon of crossing over that happens in prophase so mendel's first law depends on disjunction in anaphase but mendel's second law depends on crossing over in pro phase mendel got it backwards if you know what i'm saying because prophase comes before anaphase however mendel's first law comes before second law let's answer the question of the previous video what's the difference among kinetochore canadial plastic candidoplasty and kinetoscope kinetochore was discussed in the previous video this is the anchor protein by which the centriole gets attached to the centromere kinetoplast is a network of circular dna inside a large mitochondrion where do you find kinetoplast in a class of organisms known as kinetoplastids or kinetoplastida or kinetoplastia and these are freaking parasites such as trypanosoma kinetoscope is an early motion picture device that creates the illusion of movement kinetic basically they show you sequential images over a light source and you'll think oh actually mickey mouse is moving no it's just different pictures i have an anti-cancer pharmacology course on my website medicosis perfectionist.com you can download it today thank you for watching please subscribe hit the bell and click on the join button you can support me here or here go to my website to 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