In humans, aniridia, a type of blindness, is due to a dominant allele A. Migraine headaches are due to another dominant allele M. If a man who suffers from both conditions (AaMm) marries a woman who suffers from both (AaMm) , what are the chances of an offspring expressing both traits?

A) 9/16
B) 3/16
C) 1/2
D) 1/16
E) 4/16

To have both conditions, an offspring must inherit at least one dominant allele (A) for aniridia and one dominant allele (M) for migraines from their parents. Each parent is AaMm, so for each trait (aniridia and migraines), the chance of passing on the dominant allele is 3/4 (AA, Aa, or aA for aniridia and MM, Mm, or mM for migraines). The chance of an offspring inheriting both dominant alleles (and thus expressing both traits) is (3/4) * (3/4) = 9/16.