[Music] hello my dear children namaste and welcome to session 1 of our chapter 2 for class 10 icsc which is genetics yes let's get started and this is ambika your biology master teacher right here on this amazing platform of vedanta now you know what children to get started let me tell you this genetics is one chapter that uh most of my students in my last seven plus years of teaching experience most of my students have been telling me that this is the hardest chapter for them if it's there in the syllabus but then trust me you will get to know within the next two or three sessions that we are going to be doing here that this is actually the simplest for you to score marks so you must uh in my opinion you must consider yourself blessed to have a chapter like this in your syllabus because it's easily gonna affect you at least five marks for your uh class 10 icse board exams and personally for me it's always been my personal favorite uh chapter all you need is a little bit of extra efforts in understanding the basic concepts which we will be covering in this session and the next session and then sessions three and four which normally everyone considers the hardest parts of the chapter are going to be just super easy for you all okay stay with me and let's get started as always here is a positive quote for you this is what i have to tell you today you are only captive by walls created with your hands and choices so let's let's not imagine any boundaries at all let's not imagine any possible limitations to what we are capable of doing because ultimately if our intentions are true and pure it will definitely come out to the world okay let's move ahead and today we are going to be learning about these what are they what is genetics um variations and inheritance mutation sex determination and i'm gonna be telling you some of the important terminology which we use commonly in genetics so is it a very basic thing and does it mean that you can skip this session definitely not it forms the base for your understanding of the upcoming session and the session that's going to be coming after that as well so stay with me and here we get started look at this family members we know quite often resemble each other yet they are different what do you think is the science behind this um well although i have shown you the picture of the simpsons cartoon um which i think is a very cute one to represent this concept think about it in your own perspective think about how much you resemble your parents or how different you look um from your parents or how similar or different you look you and your siblings look from each other you and your cousins perhaps resemble each other more than you resemble your own siblings why does all this happen how does all this happen yes it is a pure science and it is the science that we call genetics there are there are a few um basic set of rules that determine what you are going to look like and how different or similar you're gonna look like each other okay so with that let's move ahead what is gene and genetics gene is the functional unit of inheritance and the study of inheritance is what we term as genetics okay so um what is gene if you look at this picture you would know uh it's a double helical structure of dna the double helical uh dna model which is there the gene is a segment of dna basically simply put now what is dna in the first place um in case you're not thorough with those concepts i would strongly suggest go back to your class nine and uh have a quick recap of all those concepts or you can also watch the videos that i have done for uh for the the chapter cell cycle and cell division wherein we have discussed this well in detail okay what is dna what is chromatin um what waters chromosome and so on okay so this is it a chromosome or chromatin biochemically is made up of dna and histones if you can recall and one segment of dna is what we call a gene so one dna one dna molecule which is here is made up of many different segments which means it's made up of many different genes and the genes are what determine our features our characteristics okay and the study is what we call genetics now how is it that something that's there inside your nucleus something as tiny as the gene is able to determine what you look like or is able to determine your characteristics this is the science behind it children this is just there for your extra bits of information in case you find it hard to understand this what's written on this slide do not worry too much about it but in case you are interested in knowing that please do have a look at it and listen to what i have to tell you in the next couple of minutes now jeans although they are found inside your nucleus it goes through a lot of um a lot of transformation it goes through a lot of modification and a lot of changes through a couple of processes which we call transcription and translation okay these are concepts that you will be doing a lot in detail in your class 11 and 12 so not to worry for the time being just understand that through a set of complex processes through a sequence of complex processes dna gets converted to proteins and why are proteins important most enzymes in our body which help in you know making the most of our metabolic reaction rates faster and help in most of our reactions in the body are they are biological catalysts basically uh they are proteinaceous in nature a lot of them okay this is why we say proteins are important and the amount of a particular protein would decide whether or not you're expressing one particular character fully partially or you don't express it at all regardless of whether or not you have inherited those genes okay can sound a little confusing i know but not to worry i'm sure by the end of the next three four sessions you will be much clearer and you will find this much more easier to understand okay so for now just understand dna gets transcribed and then it gets translated to what we call proteins and they are what decide our characteristics but then where is the base coming from it's coming from the dna or from your genes right now the entire set of dna is copied when a new cell is formed we have discussed all about mitosis and meiosis in uh chapter one so um i hope you guys are very clear about that by now what happens through interphase you know the s phase happens when dna replication occurs wherein the entire set of dna replicates itself right as a as a preparatory step to form a new cell or a new daughter cell okay now sometimes when this copying of genetic information when dna gets replicated it doesn't happen perfectly or there is some kind of imperfection that may arise when this genetic information is copied during dna replication this is what we call mutation for instance if you actually recall what we have discussed uh remember i have told you all about the the nucleus and the purine and pyrimidine combinations um a t g c right this is how ideally nucleotides would pair up at the time of dna replication but in case it doesn't happen normally sometimes it happens that a may by mistake end up pairing with g or it may pair up with c or something like that when that happens we call it mutation a random mistake a random error that can occur in your genetic material be it at the gene level as i have shown you at the nucleotide level which is within a gene or it can be um for an entire segment of genes or for a group of genes together or for the number of chromosomes also which means basically i'm trying to tell you mutation can occur either at a point level or a genetic level or it can occur in terms of the number of chromosomes also which means we call it at the chromosomal level as well okay but whatever it is when imperfections in dna copying do occur we call it mutation mutations can be either somatic mutations or germline mutations somatic mutations are those which occur in your non-reproductive tissues which means if it's not in your non-reproductive tissues they are usually not inherited it's it just happens in your body and it just goes off with your generation it vanishes but then in case it occurs in your egg or sperm that particular mutation it can get inherited by your offspring which means it can cause which means this is exactly why we say um cancer and many other diseases can be inherited right mutations we know are capable of causing diseases like cancer if it's occurring in your reproductive tissues it means it can be inherited by the offspring so these are examples of somatic mutation and these are examples of germ line mutations okay which occur in your reproductive tissue and all of this regardless of what uh what type of mutation they are we say that they cause variations okay now let's try and understand the significance of mutation and variation why does it even happen well partially or i would say most of the time variation is a very important process because as i told you mutation does create variation most of the time unfavorable mutations are selected against as in if you go by the principle of natural selection which um darwin proposed which you will be learning in detail in the chapter evolution what does the mutations which are which do not help a particular organism adjust to its surroundings or the environment wouldn't continue further which means they are selected against they just vanish but then through reproduction favorable mutations which means those mutations which do help an organism survive and get adapted to the changes in the environment get selected right so favorable mutations are more likely to survive and they continue with every generation which means i think um to to give you a better context because you haven't learned the chapter evolution i will just tell you a small story here um a llama was actually the first person to come up with the with one of the most popular theories of evolution wherein he gave the example of the giraffe it said that giraffes initially when they were formed millions of years ago they are said to have been short animals unlike the present-day giraffes so short-necked giraffes just like a goat sheep and cow they went about grazing and feeding upon plants which were like at ground level um and so on eventually what happened was that there came a point of time where food was no longer available at the ground surface or ground level so what did they do uh giraffes which um which couldn't which couldn't find any other alternative they just ended up dying of starvation but some giraffes were a little smarter and they went about trying to stretch their necks to reach leaves which were on taller trees they kept doing that and for the next thousands of years it is said that this slight stretching in the neck of giraffes kept on accumulating and this accumulation step by step step by step get got happening for over millions of years and we see the present-day giraffes which are very very long-necked right so um it is said that it is the favorable mutations this continuous stretching of neck led to a condition where there came about a mutation in the dna of those giraffes and that mutation because it was favorable for the giraffe it kept inheriting it kept on getting inherited by the offspring and that is how today we know that only long-necked giraffes survive those giraffes that did not inherit the favorable mutation ended up dying of starvation unfortunately this is why we say variation is important because it is a raw material for natural selection and hence evolution if not for variation imagine every organism that survives on this planet today would look exactly like carbon copies of each other we would all perhaps have been just unicellular organisms like the first form of life that was formed on the planet right so variation is important yes formation of new characters right as i have told you that is what has led to biodiversity helps in adaptation to environmental change as i have told you about the giraffes um character the long-necked giraffe and yes it also provides individuality to an organism although all of us you and i belong to the species homo sapiens we are still a lot different from each other why so it's because of variation that exists right okay now children before we move ahead let me list out a few problems that most of you face in online education these days i understand that many of you have been coming up to us and saying that you have a lot of unanswered doubts because you don't get to meet your teacher in person on a daily basis maybe you don't have access to systematic notes properly tests and assignments are not happening unlike normal school days competitive exam preparation is becoming even more of a challenge choice of schedule choice of language all of that is a problem but then the good news is that we have all these problems solved for you right here at vedanta and in addition to these we have a lot of 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a quick check yes basic unit of inheritance previously known as factor is chromosome gene dna cell and your time is up the answer is gene in fact factor the word factor was used uh by mendel who is known as the father of genetics to refer to the word gene and allele okay we will get to know about all of those terms in the next session so don't worry too much but then um just understand that the father of genetics himself around the time uh he was carrying out his experiments the terms gene dna uh chromosome all of that hadn't been coined yet so he went about using the term factor now dash is a raw material for evolution and natural selection inheritance variation binary fission budding yes and your time is up the answer is variation yes children variation is the raw material for evolution and natural selection most certainly okay now the branch of science with which deals with heredity is evolution molecular biology cell biology or genetics super duper easy i'm sure and your time is up the answer is the name of this chapter which is genetics now differences that exist between individuals of a species are called dash evolution mutation variation features differences that exist between individuals of a species think about the differences between me and you what do you call it as would you call it evolution would you call it mutation is it features or is it variation and the answer is variation and well done guys whoever has got the answers right rest of you don't worry at all i'm going to be giving you a lot more interesting bits of information after which we are going to be having one more quest time okay so get ready children human beings have two major types of chromosomes human beings are any sexually reproducing organism for that matter which we call optosomes and sex chromosomes okay so autosomes um are those chromosomes which do not determine the gender or which do not determine whether you're a male or female whereas sex chromosomes as the name indicates are those chromosomes which determine whether you're male or female now what you see here is the set of chromosomes of a human male cell why am i telling you it's a male cell because the sex chromosomes you can see is comprised of one x chromosome and one y chromosome what about the rest of them we have 23 pairs of chromosomes in each of our deployed cells we've learned this in chapter one and we've learned this and we've perhaps learned it in grade nine also and i've told you that we represent them in pairs that's why we call it 23 pairs of chromosomes rather than saying 46 chromosomes because literally because each of our chromosomes is in a paired condition in our deployed cells or in our somatic cells so look at that you have the first pair of chromosomes second pair of chromosomes third pair of chromosomes and so on till the 22nd pair of chromosomes you find it like normal it's it's common to every human being regardless of whether you're male or female but the last pair or the 23rd pair of chromosomes is what we call sex chromosomes which is made up of two x chromosomes in the case of a female and one x and one y chromosome in the case of a male okay so this is one important difference all of us must understand i'm telling you um with respect to a diploid human cell okay 22 pairs of autosomes and one pair of sex chromosomes okay very very very important to understand this and now with that understanding let's talk about sex determination in humans yes we know that um in the indian culture especially what decides whether a baby is going to be male or female like people generally have these superstitious beliefs that if the uh mother eats eats a certain kind of food the baby will become a girl or if she eats a different type of food the baby will become a boy and so on during her pregnancy um and there are a lot of other interesting tales that most of us would be able to relate to but then you know what the truth is the sex of a baby is determined a lot before we actually start talking about all these food items it is determined at the time of fertilization water fertilization diffusion of the egg and sperm is what we call fertilization what is the result of fertilization it is the zygote so as you can see here um the egg cell look at this this is the mother this is the father and as i told you an egg cell because the mother would always contain only two x chromosomes as her 23rd pair when gametes are found when her eggs are formed obviously these would split up apart from each other and enter into different gamete cells right so one single egg cell would contain only one x chromosome okay always an egg cell would contain only one x chromosome whereas whereas the difference comes in the case of the sperm because as i told you earlier men have an x chromosome and a y chromosome in their deployed cells which means at the time of gamete formation imagine this is the uh deployed cell which is destined to become the gamete cell through meiosis at the time of meiosis when sperms are formed these would split up and enter into different gametes which means in one ejaculation a male is said to produce a million sperms in that millions firms roughly a million sperms in that millions of sperms half of it is said to be sperms which carry an x chromosome okay the remaining half are said to be sperms which carry a y chromosome but on the contrary as i told you an egg cell or the ovum always carries only an x chromosome okay so there we go this i think has already given you the hint at the time of fertilization an egg doesn't move we know that we've learned it in reproduction in concepts like that in lower grades the sperm which manages to fertilize the egg through that race between the millions of sperms i told you the the sperm which manages to fertilize the egg or meets the egg first if it carries an x chromosome it results in a baby girl on the contrary if the sperm that manages to meet the egg first in that race if it carries a vice a y chromosome it results in a baby boy so what are we trying to say we are trying to say that the sex of a baby is decided by the type of sperm that fertilizes it basically it is the father who decides or not physically in his control of course it's purely a matter of chance but then which type of gamete the father contributes to fertilization is what decides whether the baby is going to be a girl or a boy so continuing and summarizing whatever i have told you until now here we go this is a punnett square basically what we call a punnett square in which i have represented the possible types of combination between a sperm and an over the sperms as we know the chromosomal um components of a sperm or the chromosomal constitution of every sperm would either be 22 autosomes plus an x chromosome or 22 autosomes plus a y chromosome remember they are not paired in gametes okay and in an oven on the contrary it's always going to be 22 plus x okay um so there we go look at uh the possible combinations between them 22 plus x over and a 22 plus x sperm is going to fetch you a result of 44 plus x x chromosomes which makes a daughter zygote um and this combination would fetch 44 plus xy which is gonna fetch you a male zygote okay so same thing likewise here also it's the same thing basically what we're trying to say is it's a 50 50 probability okay 50 50 ratio okay now we go on to discussing some very very important terms which are used in genetics children this is perhaps one of the most important things you need to understand to ensure that session 2 and 3 are going to be very easy for you to understand now gene what is a gene i have told you that right at the start of today's session i have told you inside your nucleus you have the chromosomes and biochemically chromosomes are made up of dna segments of dna are what we call genes okay um so there we go this is what gene is and we say it is the basic unit of heredity now comes ali where do you find alleles there is a term that we use saying alias now remember children i have been telling you about homologous chromosomes i told you chromosomes are always paired in the image i showed you some time back also i showed you the in a deployed cell chromosomes are always paired imagine this is the chromosomal pair one in this chromosomal pair one i get one member from my mother and the other member from my father okay from my mother one member of my mother's first chromosome and one member of my father's first chromosome come together and form my first pair of chromosomes they are together forming one homologous pair because they are structurally looking alike they carry copies of genes for the same characters okay so what i'm saying is alleles are copies of genes or versions of jeans i get one copy of a gene or one allele from my father and i get another allele or another copy of the same gene from my mother but only one of them is mostly expressed okay you will understand more about this as we go further into mendelian genetics but for now understand alleles are found on members of homologous chromosomes okay children now moving ahead talking about the concept of dominance and recessiveness now talking about dominance um there are some alleles which are always expressed regardless of um regardless of you know whatever the condition may be i told you uh it is an aaa example that i showed you earlier so sometimes it happens that this allele okay it gets expressed while this one small a what i am representing a small a does not get expressed the allele which does get expressed which does get expressed in any condition is what we call the dominant allele the other allele which doesn't always get expressed because in the presence of a dominant allele sometimes this allele which you see represented as the small letter here may not get expressed we call that a recessive allele okay so a dominant allele and a recessive allele in this example that you see here it's the example of eye color okay so eye color um is the character we are talking about um and the different traits under eye color eye colors may be either brown eye color blue eye color green eye color black eye color and so on so we say eye color is the character we are talking about where is blue brown black green or whatever are the different traits or the different versions of the character eye color okay traits are more specific while characters are more general okay um and here if you look at it at the genetic level one parent probably in this particular example you can see both the parents are what you see here is of parent two and this is from parent one you can see that parent one and parent two are both brown eyed okay imagine brown night parents but genetically if you look at their genetic combination you see that both of them have one allele for brown eye color and one allele for blue eye color okay both the parents parents one and parent two both of them um and look at the possible combinations of them as i have expressed here capital v capital b capital b small b a capital b small b again and the small b small b which means there is 25 percent probability of one out of four chances that their offspring can also be blue eyed which means we sometimes wonder right how can a blue eyed child be born to two brown eyed parents this is the result okay this is the effect of dominance and recessiveness um so here we find a combination of two recessive alleles which is resulting in a blue eye trait whereas look at the other three what are they in this case you see capital b capital b only two dominant alleles definitely it's going to express only the dominant trait which is brown but in these two cases also you see the brown eye color trait despite the fact that only one brown eye allele is present and the other allele which is present along with it is a blue eye color allele so despite this condition only the brown one is expressed the blue one's effect is masked this is why we call the blue one here as a recessive allele and the brown one here a dominant allele so basically here in this example you can see that when there is at least one dominant allele present yes it will be expressed physically it will be expressed whereas for a recessive allele to be expressed it has to be present in a similar pair or it has to be present along with the similar pair okay there are more terms that we have to understand which is coming up which is homozygous and heterozygous i have told you capital b capital b capital b small b and the small b small b three different conditions i have told you of uh allelic combinations when both the alleles forming a pair are similar to each other like the capital b capital b and the small b small b we call it a homozygous condition because homo means similar whereas look at this case capital b small b is a heterozygous condition hetero is different okay so what i'm saying is now let me tell you this in a combination of this and the previous slide that i have shown you a dominant allele can express itself in both homozygous and heterozygous conditions by which i say both of these would result in a dominant expression whereas the recessive one gets expressed only in a homozygous condition okay that is the basic gist of homozygous and heterozygous and about dominance and recessiveness now why have i shown you it in chromosomes it is because i told you you find alleles on the homologous chromosomes members of a homologous pair of chromosomes now coming to phenotype and genotype what is it nothing complex at all genotype is what i have been telling you until now capital b capital b capital b small b and the small b small b these are examples of genotyping whereas when i say both of these physically are seen as brown eyes and this is seen as blue eyes i'm talking about the phenotype what we physically see is what phenotype is the physical expression of a gene is what we call a phenotype whereas the genetic makeup is what we call genotype because when you look at me externally you can make out only my phenotype you can only see that i am black-eyed genotypically whether i am homozygous or heterozygous you don't know and i don't know either right we would be able to determine it only by examining my family history based on whether my parents are both brown eyes or black eyed whether their parents are both black eyed or brown eyed and so on so physically externally what you see is the phenotype but inside the genes what alleles we carry is what we call the genotype like you see in this image also the genotype you see of the mouse's fur color or the code color but phenotypically you see that it's a grayish brown colored phenotype or a color okay now i think terms like mono hybrid cross and dihybrid cross also i will uh just introduce you to them because it's coming up in the next session so mono hybrid cross is um those refers to those types of genetic experiments wherein only one character is studied at a time for instance um we are studying a plant the inheritance of characters in a plant say for instance out of all the characters that a plant has we are focusing only on flower color we are looking at only the results and combinations of flower color in our genetic experiments this is a monohybrid cross likewise a dihybrid cross is an experiment wherein two pairs of contrasting characters are studied at a time for instance in this case you see seed color and seed shape seed color can either be yellow or green seed shape can either be round or wrinkled we are studying how both of these characters or how the contrasting traits of both of these characters are inherited at a time together we are studying the inheritance patterns of them and we call it a dihybrid cross okay so here we summarize all the terms and their meanings that we have discussed what a gene is i have told you already what an allele is what phenotype is genotypist monohybrid cross um and yes dihybrid cross also um homozygous condition heterozygous condition what a traitors trait is a version of a character so pretty much um i think if you think about it traits are aversions of characters while alleles are versions of genes do keep that in mind it's a very very very important basic thing to know and i don't think most biology teachers teach that kind of a different so it's important for you to understand children you can't use them synonymously traits is a version of a character allele is a version of a gene okay and yes then coming to a die hybrid crosses i have told you pure breeding is a character that has been unchanged even after many generations you will understand the meaning of pure breed better as in more as in when we dive inheritance dominant rate and recessive trait also we have seen what it means now coming to the next part which is the quick check let's see how much of this you have understood the condition in which both the alleles are identical homozygous heterozygous mutation variation okay and your time is up the answer is homozygous wherein uh the example of capital b capital p or a capital a small b small b this is homozygous heterozygous would mean this okay alleles of a gene are found on dash homologous chromosomes sister chromatids different chromosomes either b or c okay again your time is up and the answer is homologous chromosomes yes now a dominant trait can be expressed in homozygous condition heterozygous condition both a and b absence of alleles too dominant trait okay and your time is up the answer is both a and b which means i said uh a capital b capital b and a capital b small b this is a homozygous condition this is a heterozygous condition but physically both of them are expressing the brown eye colors yes okay now great job guys if you have got all the answers correct in case you haven't not to worry at all children let me tell you the very first time i studied this chapter also it was very very difficult for me too many new things and new concepts coming into uh coming in front of my eyes and like dancing in front of me jeans alleles crossing everything seems to seem to be dancing in front of my eyes but trust me as and when um i made it a point to read more about genetics and work out more logical problems on genetics things became much clearer to me and that is how till date genetics is one favorite or rather the most favorite chapter or the most interesting chapter that i find in the entire syllabus of biology in any grade okay now you know what genetics is what are variations in mutations what is sorry what is variations and inheritance what is mutation uh how sex determination human beings occurs and all those important terms or the terminology commonly used in genetics so that's about the children but then do remember to visit vdnt dot in slash ytpro and the coupon code amb pro which can be applied to avail the best offers that we have right now in vedantu pro subscription um so children home the question before you leave jeans are two characters as alleles are to dash think about it i think i have told you uh the answer already while i was explaining this genes are to characters just like alleles are to dash okay so uh alleles are versions of genes and something else is a version of character that would be the answer okay so think about it and let's see who's giving me the answer first if you have enjoyed the session please do remember to hit the like button right now share it with all your friends who you you think would benefit from this and in case you have not subscribed to our channel hit the subscribe button right now so that you get all the updates which come up on this channel vedanto 9th and 10th english and of course the bell icon right next to it so that you keep getting notifications thank you very much children and until we meet again in yet another interesting session this is ambika signing off bye bye