A man with blood type $AB$ marries a woman with blood type $O$. What is the probability that their child will have blood type $O$?

Solution

1. The father's genotype is $I^A{I}^B$.
2. The mother's genotype is $ii$.
3. The possible gametes from the father are $I^A$ and $I^B$.
4. The only possible gamete from the mother is $i$.
5. The offspring genotypes are $I^{A}i$ (Type A) and $I^{B}i$ (Type B).
6. Hence the answer is (A).