Answer: 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.
