Genetics question HELP needed

[Psa]

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This question is from Kaplan's end of the chapter review questions and I just don't get it!

If a male hemophiliac (X^h Y) is crossed with a female carrier of both color-blindness and hemophilia (X^c X^h), what is the probability that a female child will be phenotypically normal?

A) 0%
B) 25%
C) 50%
D) Same as for a male child
E) Not enough information given

The book's explanation: Correct Answer: C "In this problem we are told that the female in this cross is a carrier of two sex-linked traits: color-blindness and hemophilia. We are also told that the genes for these traits are not found on the same X chromosome, as indicated by her genotype, X^c X^h. So in this cross, of the female offspring, half, or 50%, will be phenotypically normal.


If you do the cross between (X^h Y) and (X^c X^h), you get (X^h X^c), (X^h X^h), (X^c Y) and (X^h Y). Doesn't this show that both females will be hemophiliac?

I'm probably wrong but I just don't seem to be getting something...

 

[aznnytezx]

With this question, I did not read the explanation or your answer. I am going with C, 50%. The reason because is you know that the female will not carry a color-blindness just because the father is not color blind. Since color-blindness is a sex-linked trait, the only thing that is possible is that the female child will be a carrier for color-blindness. Since that eliminates color-blindness, we look at hemophiliac next.

We know that the father have hemophiliac, so his X chromosome will be passed to the female. So we know for sure she is going to be at LEAST a carrier. Since she will always be at LEAST a carrier, the probability of that is 100%. She will have at least one X chromosome that is hemophiliac, but the mother who can pass the X chromosome as hemophiliac or color-blindness is 50/50. 50% chance that she will pass it as color-blindess or hemophiliac, if we know this. Then we can do the probability rule, 1 x .5 = .5 x 100 = 50%

 

[dbd]

The female child with a phenotype of (X^h, X^c) would be phenotypically normal. You might notice this is the same genotype as the mother. The problem states that the mother is a carrier of both hemophilia and color blindness, meaning that both diseases are recessive. In other words the mother is phenotypically normal since she doesn't have two copies of an X chromosome with the hemophilia allele. She's not colorblind either since she doesn't have two copies of X chromosomes with the colorblind allele.

 

[athomas]

No, it does not. Your X^hX^c is NOT a hemophiliac, she only has 1 allele for that disease. She is a carrier for both, just like the mother.

 

[Psa]

So in order for a female offspring to have color-blindness or hemophilia, they need to have X^c X^c OR X^h X^h?

With this question, I did not read the explanation or your answer. I am going with C, 50%. The reason because is you know that the female will not carry a color-blindness just because the father is not color blind. Since color-blindness is a sex-linked trait, the only thing that is possible is that the female child will be a carrier for color-blindness. Since that eliminates color-blindness, we look at hemophiliac next.

We know that the father have hemophiliac, so his X chromosome will be passed to the female. So we know for sure she is going to be at LEAST a carrier. Since she will always be at LEAST a carrier, the probability of that is 100%. She will have at least one X chromosome that is hemophiliac, but the mother who can pass the X chromosome as hemophiliac or color-blindness is 50/50. 50% chance that she will pass it as color-blindess or hemophiliac, if we know this. Then we can do the probability rule, 1 x .5 = .5 x 100 = 50%

But the female offspring CAN carry colorblindness...

 

[aznnytezx]

They can carry color blindness, but they cannot be color blind. As in they only can be carriers.

 

[athomas]

They can carry color blindness, but they cannot be color blind. As in they only can be carriers.

In this particular example, the female children could only possibly have hemophilia and not colorblindness. In general though, obviously a female could have color blindness if she has both defective alleles since it's x-linked recessive.


You could also be super unlucky and get an X chromosome with both recessive alleles on it :/