2. A recessive, sex-linked allele b causes color-blindness....

2. A recessive, sex-linked allele b causes color-blindness. A normal woman whose father was color-blind marries a color-blind man, whose parents both had normal vision. a. Draw the pedigree, showing the parents of the normal woman and the color-blind man. Include genotypes and phenotypes. (2 pts) b. What are the odds that their next son will have the disease? Daughter? Draw a Punnett square to explain your answer (2 pt) c. If this couple has 5 children (regardless of sex), what is the chance that 1 will be color-blind and 4 will be normal? (1 pt)

Transcript

00:01 Alright, so this question is about a recessive sex -linked allele that causes colorblindness.

00:10 So this is going to be sex -linked, so this is for colorblindness, and this is just a normal x allele, right? because it's sex -linked, and then y doesn't have it, right? so you can't have a yb, you just have regular y chromosomes.

00:32 So we have a normal woman.

00:35 So let's draw her out like this.

00:38 And she has at least one normal x.

00:41 However, we're told that her father is colorblind.

00:45 So here's her father.

00:47 He has xb.

00:49 And the other one has to be a y because he's male.

00:52 And it doesn't really say anything about her mom.

00:56 But she then marries let's actually move her over here so she then marries a man who is colorblind so whose parents both have normal vision so then this is going to be her husband so if he is color blind that means he is also like this so whoever is affected let's color them in and both of his his parents have normal vision.

01:28 So that means her, his dad has to be just regular xy.

01:34 And his mom at least has to have the x.

01:37 So if he let's look at him first, if he is xb, that means and y.

01:43 So the y comes from dad, the mom had to have given this xb.

01:49 So that means the mom definitely had one xb be x, right? because this means that she is a carrier.

01:57 So this is half shaded in because she's a carrier.

02:00 Now the person we are looking at is this person.

02:03 This is her person of interest for this problem.

02:05 And if she got one xb from dad, right? because she couldn't have gotten the xy.

02:12 So if she got this from dad that means she definitely got this x from mom so we don't really know what mom is we don't really know if mom's a carrier but she doesn't necessarily have to be right because this is the one that she got from dad and she is also a carrier now if she or or this is going to be part a.

02:39 If they have a son, this is going to be xxb and xby.

02:49 We have a punnett square, right? so this is her here and then this is him here.

02:59 So let's just do this punnett squared.

03:02 We get the x from her, the xb from him.

03:06 We get the here we get x b from her and x b from him and then for down here we get x and y and then here we had x b and y so let's see the question is asking what are their odds that their next son will have the disease which ones are the the suns.

03:32 The sun is going to be xy.

03:34 So we get that from over here...

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