SENIOR SECONDARY BIOLOGY ECZ SYLLABUS HOW TO APROACH QUESTIONS ON GENETICS

welcome to today's lesson in this video we're going to look at how to approach questions on genetics and this is biology 1590 following the examination council of zambia syllabus so please stay tuned as we show you on how to approach questions on genetics now questions on genetics they come always in paper two section a and it's usually the last question which is question five in section eight so i've made a uh i've compiled from a number of examination questions past examination questions and i just want to show people on how we can approach these questions okay so the first question reads pure breeding dwarf garden bee plants we are crossed with pure breeding tall garden tea plants the resulting offspring we are all talk what is meant by pure breeding two using your own symbols state the genotypes of the parents be using a genetic diagram show the cross between a dwarf parent and one of the offspring so now it is very important that we analyze the questions as we go through so here are some keywords so with this one if you are breathing you know what that dwarf here then we also have another word here as you can see this is to pure breeding then so these words are some of the keywords that you can use to answer the question including this word here of springs okay so we'll start by explaining what the word pure breeding means now pure breeding uh the other name for this pure breeding is what is called homozygous so the other name for pure breeding is homo zygas okay now what does this mean so pure breeding uh simply refers to an organism or an individual having the same type of values or genes at the same locus the same types of alleles or genes at the same locus that's what pure really means as you can see the other way for pure breeding is homozygous so homo means one or simply same so homozygous okay so now since we have been told to say uh this dwarf guardian viewers homozygous and the dwarf when we are writing the alleles we there are two types of values there is what we call a dominant value and what we call a recessive allele now the symbol for a dominant value in genetics is always a capital letter then the symbol for a recessive value is a a small letter so here since they say dwarf which means short so we are going to use the smaller dance so the small letters we are going to use is t and t okay that is for the dwarf and then for the two here we are also going to use because it is homozygous or rather cure breathing we are going to use capital letter t and t okay so we we've already answered question a because we are saying pure breeding refers to an individual or organism having the same type of values at the same brokers okay so we go to two which is saying using your own symbols state the genotypes of the parents so the first one we have to where we are supposed to state is the pure breeding group that mp has already figured out this one will be small letter t and small entertain then we go to the door and this one will be capturing the t and capital t okay since the question is saying that these two were across this one and this one we can quickly use a permanent square just to see how the crossing was done so we are going to cross the toe one and the short one so usually for just determining the outcome or having an idea of what and what you're crossing we use a finite square so a finite square works pretty much like a multiplication time table okay so it's simple like that so we are going to say this t multiplied by this t here we are going to have t and t then here we're going to have this t and the small t so here we have the capital t and the small t even here you're still going to have the same thing okay so what is going on going on here easy this team would play by the team you have that this team would play by this one you have that this one multiplied by that one you have that one so you can see that all the resulting offspring there we are heterozygous tau so this is calculator t and the small letter t okay so using a genetic diagram show the cross between a dwarf parent and one of the offspring so as you can see they have said a dwarf parrot now the black parent you know it's t and t then one of the offsprings here figured out that the offspring they have a t and a g so these are the two that we are crossing and four is five let's see how we can perform the crossing so just a reminder the correct answer for question a was supposed to be written like this so if you are reading reference to an individual having two copies okay two copies of the same value at a locus for example this is what has been given so that is the answer you're supposed to fill in there now let's do let's do a genetic crossing here so like i said genetic diagram this is what i'm about to demonstrate so here what are we crossing so on top here you can just write what we are crossing is a dwarf parent okay so this is a dwarf parent that's what we are crossing dwarf parent so we are crossing a dwarf parent and one of the offspring here okay and the offspring that is what we are crossing so i'll just write this one offspring here that is what we are crossing okay so now here all these that have written here you have to write them in exactly the same order that i've written you have to write a parental phenotype so phenotype is just uh phenotype is just the uh the physical appearance okay the physical appearance so physical appearance here phenotype we know that this one is a dwarf okay so you just write dwarf that is the appearance okay then for the offspring here the phenotype what we can see is that it is what it it is talk okay it is talk now here on the parent genotype so we are just going to write t and t then here we're going to write this t and that's t it's a problem this is what we figured out then here on the column for gametes it means that you have to write them now one by one you've seen i've separated here they are together i've written them one by one these are together so i'll also write them one by one so i'll write them one by one like that then i now begin to cross so across this one here this one here is gone across with this one so you start with the calculator so it will be t and uh t like that okay then this same one also it should be able to cross with that one then here we are having uh so we are having a t small letter t and smaller t because it is this one and that one then we go to this one so here we are having this one and that one crossing together we start with captivator t and the t there then we also uh go this same one here it also has to cross that one so that we have t and small letter t so here make sure that the f1 generation is slightly on top here so that this genotype is directly corresponding with this one then here under phenotype you you can just go ahead and be writing this t and t there it means the toe then this one here it will mean dwarf okay this one means then this one will mean okay then this one will mean dwarf okay so this one will mean dwarf so you can even write the genotype ratio if you want so let me just write it the genotype ratio here g error which will be equivalent to 2 capital letter t and this small t then two uh two t t that's what we have here then this one means if phenotype ratio it will mean two toe to two that's what is going to mean okay so that is how you answer such a particular question okay we proceed we go to another question that came in another year the question reads uh two farmers one with a pure breeding again we are still dealing with a pure breeding so two farmers one with a fewer breeding black bow so here pure breeding black bow and the other with a pure breeding white cow decided to cross their kettle the black bow was crossed with the white cow and all the resulting offspring had a court color called ron so this is a completely new color none of the offspring were either black or white why because uh both they were they were both dominant so both jeans were dominant so this is a situation which we call core dominance where the chart the offspring that is born uh looks neither like the father nor the mother but it is a hybrid that is produced so a hybrid is a result of what we call co-dominance meaning the gene from the father and the gene from the mother they are both uh they are both strong they are both dominant so because they are both dominant they are going to share on how their characteristics are expressed so that is what we call what codominance okay so here the fact that they've told us you are building blackboard we can come up with it b and capital letter b okay that is just from our head then for white here uh a white cow here we know it will also be calculated w and capital letter w okay so now let's try to answer the questions before we get ahead of ourselves the question reads using letter b for the allele for black quote color okay so using letter b for the value for code color meaning what we did here on top here it is actually correct okay and w for the audio for white chord color state the genotype of the offspring so now this is what i said if the offspring because here it will mean that they had crossed b okay b i'll use a finite square like i always say a finite square is used when you are crossing uh when you're just trying to identify something for fast fast but there's a part where they use they require you to use a gener a genetic equality diagram despite the results being the same but in the example giving answers you use a genetic diagram a finite square is just used when you're trying to find the answer like in the multiple expressions or you want to determine which one is there uh which one is the correct combination okay so here we can have the w as b and w then also b and w so that we have b uh w okay we also go down there b and w then we are going to have b and w even here also it will be b uh w so this simply means that all the children they are going to be bwbw that is the genetics that's the the genotype okay so show the genotype of the offspring so the answer they wanted here was z b w okay two explain why neither the boom nor the cow had their coat color expressed in the phenotype over offspring so the answer here is because both the genes of the black bull and the genes of the white cow we are both dominant okay so the reason is very simple both the genes of the black book and the genes of the white uh the white cow we are both dominant resulting into what is known as core dominance so that is the answer that you're supposed to put here okay we continue now they're saying using a genetic diagram predict the chances of the second failure uh f2 uh second figure which is f2 offspring having a run caught color when the apparent black bull was crossed with one over one offspring so what are they saying here so here you start you follow the same order as parent phenotype transparent genotype gametes then this time around instead of having f1 we're going to have an f2 generation because an f2 generation for example if me uh if me i had children those children would be called my f1 generation then if my children have other children then those children are going to be called the f2 generation of me okay so since here they are telling us that the parent black boo was crossed with one of the wrong offspring so here you're just going to write okay here on the phenotype so you can write here as usual you're right there black bull so you can just say black or or you can just say boom okay you can just say the boom then here on the cow here you just write cow since a cow is the female who is the mercy right then on parental phenotype but the phenotype is what we can see the observable features of an organism like color in this case so here we are writing black okay so this one here what we expected to write is black okay then on the cow here we are expected to write wrong because all the offspring that we have produced at that time where ron okay so now this time go to parent genotype we know that the bo was b b okay it was pure breeding okay then the wrong one here we know that it's b w so that is a genotype then garments you just have to write them one by one so this b and that b then that b there and the w so you write them one by one and you go to crossing now so it means that this one here is crossing with that one so we have our b and b so meaning this b and that b then this same b here it also has to cross with this one here so that we have our d w okay we go to the second one this one has to cross with this one so that we can have b and b then this same one here has to cross with this one so that we can have our b and w okay so having written this this one should be correlating like that then on phenotype we're going to write this one easy black okay so you write the full black here okay when you go to this one this one is run okay so this one is it run and from there this one easy black so black then this one is also wrong so you're right this is your run okay so that is it the run there now let's just read the question they are saying using a genetic diagram predict the chances of the second failure of spring having a run caught color so what are the chances here so now chances uh you use the phenotype because they're talking about ron ron is a character so that's phenotype so you just check now how many uh remember when you're dealing with chances you have to look at the total that you have more like probability so probability is equal to the favorable or desirable outcome divided by the total outcomes so in this situation here what you're going to do is very simple you are just going to count the daughter which is one two three four okay and how many run do we have we just have two so we have one and the two so this one will be two out of four so the chances to find the chances here it could be two out of four then we can express it in terms of percentage you just multiply it by hundred so this one here one uh that one there 25 okay so here we have 50 chance okay so the answer that we are looking for here is 50 chance so chance is best expressed in terms of what percentage don't leave it as a fraction but if they ask for probability you can leave it in fraction form if they ask for a chance make sure you leave it in this form which is it 50 chance and then you have to really show what you are doing okay so having done that remember like we did in the previous you can do that the genotype ratio which would be like 2 b b okay 2 2 b w so that is the genotype ratio then the phenotype ratio you write the four words not initials but the phenotype ratio here it will also be two black okay two black uh two two run then after you do this that's when you go ahead now to calculate the yt the chances so it will just be 2 out of the total here which is 4 then multiply by 100 and you find your answer so we continue with the next question the question reads mrs mumba delivered a baby girl in a certain hospital he says mumbai has blood group all and the father to the girl has blood this is the hospital for giving her a wrong baby whose blood group was or explained using a genetic diagram why mrs mumba would win or lose the case so to start with here they are saying this is mumbai has blood group so this blood group 4 means that if the genotype can only be i or i o or is always recessive so this is the only genotype that it can have and they are saying the father to the girl has black group a b and blood group a b this one is only i a i b this is the only thing that the only genotype that can exist so the eye here is always there so whenever you are dealing with a blood group because of the immunoglobulin that's why so make sure that you put the eye whenever you are dealing with the water the blood groups because this is uh part of the blood group system okay so here now we are saying the baby here okay the baby was blood group oh so in order for us to know whether the baby was really blood group or or not we have to check uh the genotype so now since they want us to use a genetic diagram so we go straight to doing a genetic equality diagram so here we are going to right now uh uh here we write for mrs mumba so this is mumbai here let's have mrs mumba okay and mrs mumba we are saying [Music] himself now so we have mr mumba who is the father who is supposedly the father of the child so this is mrs mumba and we are going to put uh this is group a so this is group a okay so we we write now the genotype so the genotype here this is now where we put i o and i o so these things have to be in your head then we write also here we write i uh a and i b so i a ib then we go to the garments garments it simply means you have to write these things one by one so the first i o there you go to the next i o then from there you write the i a then from there you go to the ib so right here i'd be like that then we start crossing so we cross this one which should be close to this one so a is always dominant and o is recessive so we'll start by writing i a and d i and o that is what we have then this same one here should be across this one so that here we are having now i b so i b then i o okay then we go to the second one this one should be able to cross with this one and we are going to have i a and i o so i a i o then from there this same one here should be crossed with this this one so that we have uh ib ib i o so having crossed that one we can now uh having crossed that one we can now so this this this one should be alongside here then the phenotype here we can see that this one is black with a this one is so from this one you can tell to say it was not possible for this couple here to have a baby with blood group this is not possible okay so using this one now you can even write a comment using uh crossing the blood type of mrs mumba and mr mumma it's not possible for them to have a blood group which is all therefore mrs mumba would win this one who'd win this case because she was very sure it's not possible to have a blood group or because of the father okay so the only way it would have been possible the correct general type of the actual father may be if mrs mumba will be uh this black book then mr mumba or z uh maybe i a i oh this one is possible because when we cross this one even when just try using a component square let's try let's try first first so we have i o here and we have i o in here we maintain so this is mrs mumba then we we try this one i a i o so you try it you can just guess so we're using a finite square like i always say we use a planet where we want to just figure out something fast fast but when they say genetic diagram we go using the genetic diagram that we are using so here as you can see you're going to have something like i a okay i o then here we are also going to have i a then i o okay we go to the bottom one here we are going to have i o i oh because remember it's more like multiplication table this one takes that one that one then that one times that one they're also going to have i or i oh so from here you can see there is a 50 chance that this could be the father this would be the correct genotype of the father so on your answers here you can write one of the answers is i a i o the other answer you just write one of them so the other answer can be i be okay ib then i o or you can also have i o [Music] i o so any of these is the correct answer because when you cross them with with mrs mumba at least the child there will be a probability that one of the children is actually like okay let's deal with the last question in this session and i'm sure uh will be okay to write to answer any questions under this topic okay so ah blood good blood group inheritance in humans is controlled by three values ia ib and i o using appropriate genetic symbols draw a genetic diagram to explain the possible blood groups of children whose parents are both heterozygous so are both heterozygous for their blood groups their father being a and their mother being blood so since there are heterozygous hetero simply means two different so when you look at uh blood group a blood group a has got two possibilities there is where we have i a okay is i a i a and there is where or where we have now i a i o so these are the two possibles for this one then also for blood group b also the two possibles are ib okay so i b i b or where we have i b i o so these are the two possibles now here because the letter is the same it's b b so this one is called homozygous but this one is it b and o meaning it's hederating zygas then even here this one is iaia this one is homo zygas but this one has got i a and i o meaning this one easy heterozygous okay so that's the beauty about this thing now we want to show the crossing meaning we are showing they are saying whose parents are both heterozygous so meaning we are crossing i b i o and d i a i o that is what we are crossing so here uh so here they have said the father so the father is the one with a then the mother is the one with b so let's try it so here they are telling us here if we write father so we have father here than me the father according to the question they are saying the father is a so the father here under the father the phenotype we are writing that it's blood then here on the mother okay let's deal with the mother also so under the mother we know that this one shows blood group b then the genotype this is now where we write our i a i o so we show that these are heterozygous then even here we also write i be i o so this is also heterozygous then the gametes we write now i a write them separately then i or i and then i oh so we just write them separately so this one is this one this one that one this one that one that one is that one then we start our our crossing okay so our crossing this one will cross with this one then we have i a ib so i a i b then this same one here across with this one so that we have i a i o so i a i o we go to the second one this one will cross with this one so here we have id id then i o then this same one will cross with this one so that we have i o i o i o so this is what we have i o i o so here under phenotype we're just writing this is a b blood group a b this is blood glucose [Music] then this is blood group e and this is that goku oh so this is what we have okay now here our question was just telling us um using appropriate genetic symbols draw a genetic diagram to explain the possible blood groups of the children whose parents are both heterozygous for their blood groups okay the father being blood group a and the mother being like b so we have just done this is how it is supposed to be done okay now question b reads using a name example explain continuous variation so this question is different from when they just say it's uh define continuous variation but here they're saying using a named example explain continuous variation so in here you are going to say for example height in human beings is a type of continuous variation so in continuous variation there is a complete range of measurements from one extreme to the other so you see this one is an explanation if they just say define continuous variation would have just said they would have said continuous variation is a type of variation in which there is a complete range of measurements from one extreme to the other so the way you phrase your answer matters so make sure that you phrase it correctly so uh blood groups in humans is a type of discontinuous variation so in this type of variation an individual falls into a number of distinct classes or categories you are either or you are either or or not so that's the way it is when you talk about black groups here you say that you're a black group a or your blood b or a b you cannot be in between so that is this continuous variation but in continuous variation you can be able to make something that is continuous for example height you can put a short one the one who follows the next one until you put them in a certain order that is continuous variation okay so thank you for listening hope this will help hope this one will help you in your exams because we've literally covered different types of genetic questions that can be brought in your exams so please subscribe to this channel and be helped in terms of revising for your exam thank you so much until next time