A man with hemophilia (a recessive, sex-linked condition)...

Name: A man with hemophilia (a recessive, sex-linked condition) has a daughter of normal phenotype. She marries a man who is normal for the trait. What is the probability that a daughter of this mating will have hemophilia? That a son will have hemophilia? If the couple has four sons, what is the probability that all four will be born with hemophilia?
Uploaded: 2020-10-28T21:06:38-08:00
Duration: 7 min 56 s
Channel: Nicole Hewett
Description: A man with hemophilia (a recessive, sex-linked condition) has a daughter of normal phenotype. She marries a man who is normal for the trait. What is the probability that a daughter of this mating will have hemophilia? That a son will have hemophilia? If the couple has four sons, what is the probability that all four will be born with hemophilia?

A man with hemophilia (a recessive, sex-linked condition) has a daughter of normal phenotype. She marries a man who is normal for the trait. What is the probability that a daughter of this mating will have hemophilia? That a son will have hemophilia? If the couple has four sons, what is the probability that all four will be born with hemophilia?

Transcript

00:01 In this question, we're told that a man who has hemophilia has a daughter who is unaffected by hemophilia.

00:09 And then we're asked a series of question about the probability that this daughter will have children who are affected by hemophilia.

00:17 So first of all, we have to remember that hemophilia is a sex -linked trait when it's carried on the x chromosome.

00:27 So the father of this woman that we're going to be speaking of has the genotype of an affected x and a y.

00:38 And hemophilia is actually recessive, but because men only have one x, if they have an affected allele on that x chromosome, then that even if it's a recessive allele, it will show up.

00:54 The phenotype will be expressed.

00:58 But in this case, he has a daughter, and the daughter is unaffected.

01:05 We know then that she must have at least one normal allele for hemophilia because that is the dominant trait.

01:19 And because she receives one x from her father, and the only x her father has to give is an affected x.

01:29 She actually has one affected x.

01:31 So she's a carrier for hemophilia.

01:38 She's a carrier.

01:40 Okay.

01:41 So in the question, we're told that this woman marries a man who is unaffected by hemophilia.

01:52 So here's this woman.

01:55 And then she marries a man who is unaffected by hemophilia.

01:59 So he has the dominant trait.

02:03 And he has why.

02:06 And so we're asked the likelihood that their children will be affected.

02:12 So let's look to see, let's do a punn and square here to see what the possible gamut combinations are.

02:24 So going across the top, we have two dominant x's.

02:30 So this would be a daughter who is unaffected by hemophilia and is not a carrier.

02:36 We have a dominant x and a y.

02:41 So this would be an unaffected male child.

02:47 Then we have one daughter who would be unaffected but is a carrier for hemophilia and a possibility that there would be a son who is affected by hemophilia.

03:06 So now we're asked, what is the likelihood that, that this couple will have a daughter that is affected.

03:18 This is the father and then this is the mother...

Question

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