hi everybody and welcome back to miss angler's biology class i am miss angler and in today's video we are going to look at a genetics exam question this one is on a medium difficulty not too tricky it does have a little bit of technique involved as well as a bit of a dreaded explanation question we often struggle with explaining why we inherit certain things so if you'd like to attempt the question you can pause the video now before i get into breaking down the answers also if you're new here don't forget to give this video a thumbs up and subscribe and make sure your notifications are turned on because i post new videos every tuesday and thursday and also if you are in matrix and you are looking to dramatically improve your marks and get that extra edge you should think about joining my membership my membership has a whole bunch of amazing perks things like my cheat sheet summary notes which makes studying so much easier live lessons and so much more you can join via the join button on my home page so let's get into this exam question and let's read through the details so we have a pedigree diagram in front of us and it says that it shows the inheritance of color blindness in a family color blindness is sex-linked which is important for us to know and it is caused by the recessive allele with a lowercase d the ability to see color normally is caused by the dominant allele capital d so they've given us some important information the first piece of information that's really important to us is that this is sex linked and the second thing is they've provided us with the letters now you'll notice that they've said it's sex linked but nowhere have they actually given the chromosomes the sex chromosomes and they do that sometimes to make this a little bit more difficult so that keeps you on your toes so at this point you should know that if it's sex-linked it's going to be on the x chromosome and that means that we are going to see either a capital d on the x chromosome or a lowercase d on the chromosomes and so that means that if someone has a capital they will have normal vision whereas if they have a lowercase d they will be colorblind so we want to keep that in mind as we make our way through this question so the first question asks us to calculate how many of the male offspring of parents one and two were normal all right so let's just actually highlight all the males um of parents one and two males being the squares and they're normal meaning they have normal color um sight and so we've got one male over here and we've got another one over here we're not going to include this individual because he is not a son he is a man that has a child with one of their daughters but he is not one of their offspring and we're not going to include this man either because he is a son yes but he doesn't have normal vision so when the question says how many of the male offspring of parents one and two were normal we are going to say to then moving on to our next question it says state the genotype of individuals two and individuals five now a step that i've perhaps skipped in the beginning here now that maybe you'd want to go back and do is i would go back and fill in everybody's alleles just to make sure that i know who is who and that we don't um make a mistake during the exam and what i mean by that is because this is sex linked what i would like to do is i would go back and i would fill in let me just change my pen i would go back and i would fill in all of the sex chromosomes first so i would put in all the x's and y's um for our numbered individuals because generally those are the people who we are working with that's the clue to know that we don't have to do the rest and then i'm going to go back and include their letter capital d or lowercase d remember those are our important letters that we need to fill in here to get this right so we have number one individual one he is a male and he has normal vision which means that the only possible lettering that can be there is a capital d if we look at our female she has normal vision which means she has at least one capital d but we'll get back to what her other letter is soon we look at their daughter again their daughter is normal vision so she has at least one capital d um and then if we go over to individual four she has normal vision so we're going to give her a lowercase d and then we go to female 5 and female 5 has color blindness which means the only way that's possible is if these are two lowercase letter d's so now we need to go back and fill in the possible um alleles for two and three although we don't necessarily need three at this point but um if we fill in for mom we need to figure out is she a capital d on this other x or is she a lower case d which one is she going to be so in order to figure that out we can actually calculate that by looking at her children now the fact that and i'm just going to erase some of this um so that we can get rid of these blue marks there we go and so what we need to do is we need to calculate backwards what um she is based off of her children now the fact that she has an affected son which is the son over here it can only uh lead us to the fact that her other x chromosome carries a lowercase d because that son who was affected would have gotten his y from his dad and he would have got his x from his mom and that means the only person he can get that x from is his mom which means that she would have given him the color blindness and so now that we've worked that out we can go ahead and actually answer our question down here for question uh 2.1.2 what is the genotype well number two is going to be x capital d x lowercase d and individual fives genotype is going to be two lowercase d's then moving on to the next question it says a person with a recessive allele for color blindness may not be colorblind explain why males with an allele for color blindness are always colorblind now in order to answer this adequately and for four marks you are going to need to like make a statement and then give a reason and then make another statement and give a reason and essentially what we need to do is first of all we need to state that this particular allele is found on the x chromosome that's the first thing and then we need to say that the fact that males only have one x chromosome because of this they either have the dominant allele or they don't have the dominant leon they have a recessive allele which means that therefore if they have the dominant allele they will always be colorblind and that's how you're going to explain it by making a statement like it's on the x allele and the reasons that follow that is that males have only one x and then you make a statement by saying that if it's a dominant allele they'll have it if it's a recessive they won't and therefore the dominant alleles always have it therefore males always have this disorder let's move into the next question it says if individual five marries a normal male what percentage of their daughters will have an allele for color blindness but will not be colorblind so we've got some key pieces of information here number one she is having a child with a normal male which means that his um sex chromosomes will have a capital letter d on the x with a y and the next thing is we need to calculate percentage of the female children of the offspring that will carry color blindness but will not necessarily be colorblind so the quickest way to do this is to create a just a rough punnett square along the side of your page because it doesn't actually require you to show your working out and so you're going to do this alongside here and we know that individual five is colorblind so she's got two lowercase letter d's so if we quickly do the punnett square so we can do the working out we'll be able to see what are the chances what is the percentage chance of the female children so we've done the calculations now we can go back and let's just make sure that we only work with the females which means we're only going to work with this individual over here and this one over here because the other two are males and so getting back to it the question says out of the daughters how many in what percent will have the disorder well out of the daughters both of the daughters have um the allele which they do this is this lowercase d which means therefore 100 100 of the daughters have the allele or have this particular grouping of alleles please be very careful when you answer this it's often misanswered because you answer as all the offspring but you're not you're answering for just the daughters so you're not including the sons some of you may just automatically write 50 because you know it's two out of the four children but no the question is referencing of how many um of the daughters what percentage of the daughters will have the colorblind allele but not be colorblind now here is the memo for you to go over and to check your own answers and just see how they've structured out the memo i would like you to just pay um some attention particularly to 2 1 3 and how they've answered it note what they have um allocated marks to and so that you two can get those full marks for these last these like longer questions now i hope you've all enjoyed this video and don't forget to give it a thumbs up and i will see you all again soon bye