Hemophilia is a sex-linked recessive genetic disorder. Suppose that the mom has
hemophilia and the dad is healthy.
a. What is the probability that these two parents would produce offspring that are
healthy? (4 pts)
b. . What would be the sex of the offspring with hemophilia? (2 pts)

a. 50% or 1/2     b. Male

Explanation: We'll be using the symbol X^h for an affected (has hemophilia) X chromosome and X^H for a non-affected (doesn't have hemophilia) X chromosome.

The mother has two X chromosomes, and since she's affected and hemophilia is recessive, she has the genotype of X^h X^h. The father has an X and a Y chromosome, and since he doesn't have it, his genotype is X^H Y.

Set up a Punnett square with X^h X^h on one side and X^H Y on the other. It should come out as 4 offspring with the genotypes X^H X^h, X^H X^h, X^h Y, and X^h Y.

Again, since hemophilia is recessive, they have to have a genotype of either X^h X^h or X^h Y to have it. Two of the offspring do (X^h Y and X^h Y). This gives the odds of 2/4 or 1/2 (50%). Both of these offspring have a Y chromosome, so they are male.

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