A woman with normal blood clotting ability whose father was a hemophiliac and wh

Question

A woman with normal blood clotting ability whose father was a hemophiliac and whose mother was normal with no family history of hemophilia marries a man whose blood has normal clotting ability.

a. What is the probability that their first child will be a daughter with hemophilia? Round your answer properly to 3 decimal digits.

b. What is the probability that their first child will be a son with hemophilia? Round your answer properly to 3 decimal digits.

c. A man who has an X-linked dominant allele will pass it on to (pick all that apply)
All of his daughters
Half of his daughters
Half of his sons
All of his sons

Explanation / Answer

a)1/4=0.25

We know the male genotype must be XhY since he shows the hemophilia phenotype. A normal female can have the genotype XHXH or XHXh. However, we know this female must be XHXh (a carrier) since her father had hemophilia - she inherited his X chromosome. Thus, we can set up a Punnett Square. Thus, in the first filial generation, 50% of the offspring would be hemophiliacs and 50% normal. 50% of both females and males would be normal and 50% hemophiliac. The results show: 1 boy hemophiliac, 1 girl hemophiliac, 1 normal girl, or 1 normal boy.
b)Potential hemophilia 'carring' son without hemophilia: xyHh
c)a. all of his daughters

With a son, the father would pass on his Y chromosome and the mother would pass on one of her X chromosomes.

If they were having a daughter, the father would pass on his X chromosome, and the mother would pass on one of her X chromosomes.

So since the father only has 1 X chromosome, the X-linked allele will be passed on to all of his daughters. None of his sons would receive the allele, because the dad will have passed on his Y chromosome to them.

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