hi everybody and welcome back to miss angler's biology class i am miss anglat and in today's video we are going to be looking at a genetic exam question this one is a little bit more tricky it's based off of a hemophilia pedigree diagram i'm going to walk you through how to interpret the diagram as well as how to answer the questions for full marks if you are new here don't forget to subscribe and like this video and make sure your notifications are on so that you receive the freshest content every tuesday and thursday and if you are in the trick and you're looking for extra help and you want to get that distinction at the end of the year you should think about joining my membership i have exclusive members only videos we do live lessons and you'll have access to my summary notes it's at this point in the video that if you want to attempt the questions pause the video now before we run through the questions so let's get into breaking down this question now the question says that the pedigree diagram below shows the inheritance of hemophilia in a family and the allele that causes hemophilia is a allele found on the x small h and the normal allele is x big h now what they're expecting you to know here is two things one they expect you to know that hemophilia is sex-linked and the clue that this is sex-linked is because it's on the x chromosome and the second thing that they expect you to know is that it is recessive which is what they've shown over here where we have the lowercase h and they expect you to know that um sometimes they won't even give you this information in exams they want you to know this already and you will need to provide these alleles without being prompted now my advice to all matrix whether you are an a student or a d student and you're getting 80 or you're getting 40 and 30 is that you always need to go through your pedigree diagram and fill in every single person's set of alleles now you probably think wow that's really time consuming but you've got to see the bigger picture if you make sure that you understand the pedigree diagram well and you go through and you fill in everybody's alleles you will reduce the chances of you making a mistake later on especially when you are looking for people's genotypes and you're trying to explain how they've inherited it so my advice to everybody when you do a pedigree is to go through every individual and the first thing you're going to do is you need to decide is this a sex-linked cross or is this an autosomal cross now this is a sex-linked cross which means you can go through to each person male and female and you can insert the x's and the y's next to each person so that at least you already know who is male and who is female i want to quickly fill that in now before we continue now i've gone in and i've added everybody's sex chromosomes x and y for male and xx for female now what we need to do is we need to go through this family tree and fill in the obvious people first the easy ones first and then we will work our way backward and fill in all of the missing pieces now first things first the easy thing to go around and fill in is all of these hemophiliac males because in order to be a hemophiliac male you only need one recessive allele because you only have one x so that's all you can offer so that means that all of these males that are colored in so these are these squares that are colored in black they each have a lowercase h on all of their x's right and they were really easy to fill in then we have this one female down here number 14. now she has hemophilia and the only way that that's possible is if she has two lower case h's on each one and yes it is unusual to see a hemophilia hemophiliac female in a pedigree diagram but i want you to know that these are hypothetical examples so you just roll with it even though your textbook might say hemophiliac females aren't born you're just going to roll with the question and you're going to work with it as you see it now going back to all the males that are not infected or affected by hemophilia they need to have a capital h on their x because they don't have a backup h they have to so if they're not affected every male that's a square here that's not colored in should have a capital h on their x and i'm just going to fill it in quickly on all of them right now that we've done that for all the males let's do the females and the females are a little bit more tricky because they can be carriers of hemophilia which means they don't have hemophilia they are normal however they are carrying a recessive allele for it now to determine these types of things we need to look at sometimes the offspring and then we can calculate what mom and dad are now for example if we look at individual number two the mom at the top here she doesn't have hemophilia she's not colored in which means that at least one of her exes has a capital h on it now what about her other eggs well now let's look at her children okay she has two sons uh that have hemophilia which is six and seven now the only way that that is possible is if they inherited a small h from their mother because uh if they're boys they only get wires from their dads so that means that her other x must carry a lowercase h on it the recessive allele um now let's look at her daughter number four number four gets one x from mom and one x from dad now the only x that she can get from dad carries a capital h right now her other x and this is interesting she can either get a capital h from her mom or she could get this other lowercase age now the only way to know what is her other letter is to look now at her children and already i can see that her child number eight and child number nine both have hemophilia and the only way that's possible is remember if you're a boy you get your y from your dad and your ex from your mom the only way that they can get a lower case h is if they get it from their mother which means their other ex comes from their mom with a recessive allele now likewise with girl number 11 she's going to have a capital h because she doesn't have it now this is a tricky one for number 11 because she could have a recessive allele from her mother or if you actually look here she could have a capital h from dad and a capital h from mom we don't know because she hasn't had any children and the same can be said for individual 12. she could also have a capital h capital h or she could have two capital h and a lowercase h but remember they haven't had children so we can't determine that now that we've filled all of this out we can now look at our questions and answer them accurately so here we see the phenotype of individual four so here is individual four we know that pheno means physical and she is a normal female she doesn't have hemophilia the second question says the genotype of individual two and conveniently we have already calculated it so we can write that down then it goes on to say explain why females have a smaller chance of suffering from hemophilia and this is for three marks now when you are describing these kinds of answers please grade 12s do not talk about males do not say that males have this and this is why they get it more that's what we call answering in the negative you need to only talk about females so you're going to say for the three marks first of all what is a female's sex genotype she is xx so she has two x's and in order for her to have the disorder she would need the recessive allele on both her x's because if she only has it on one the dominant allele will mask the recessive allele so you get one mark for saying that she's got two x's you get one mark for saying that the recessive allele must be on both and you get one mark for saying that a dominant allele will mask the recessive allele if it's present now the final question says represent a genetic cross so we're going to do a whole genetic cross with p1 and f1 and all of the punnett squares and the phenol and genotypes and we're going to calculate the percentage chance of individuals 13 and 14 having a hemophiliac sun and so at the very end of this you must make sure that you provide the percentage and this is the percentage chance of having a hemophiliac sun now i'm going to show you what that looks like now in the memo now here is the memo as we discussed but i want to just bring your attention to the punnett square and the genetic cross at the bottom here and how we actually um plan it all out now as you can see here we've got the basics we've got the p1 we've got the parental generation we've got the genotype we then write gametes and we put our gametes down and we put our punnett square and you'll see you get one mark for each of those um and then you'll notice at the bottom here we are doing the phenoen genotype and specifically there's something called a compulsory mark here which means that you have to get this right otherwise you can't get seven out of seven you'll just get six and so when we do the calculations as you can see here we've got two females that are normal okay they don't have the disorder and then we have two males that do have the disorder so when we do the genotype and the phenotype we need to provide a percentage specifically the questions asking for the phenotype percentage and in this example there is a 50 chance of there being a hemophiliac sun or two out of five remember we don't leave it as a fraction we want to make it a percent now for those of you who are new to these kinds of memos i just want to bring your attention to this bottom bit over here you see it says you get one more for saying p1 and f1 and one for meiosis and fertilization that's what they mean over here with these like curly brackets those are saying together you get a tick for each of them but in this particular question you can get a maximum of six for the working out but the one compulsory mark is this one down here giving us the percentage chance now if 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