Final answer:
When a man with AB blood type marries a heterozygous woman with blood type A, 50% of their offspring would have blood type O.
Step-by-step explanation:
When a man with AB blood type marries a heterozygous woman with blood type A, their offspring can have different blood types. In this case, we are interested in the percentage of offspring with blood type O. The blood type O is a recessive trait, so in order for a child to have blood type O, they must inherit two copies of the O allele, one from each parent.
The man with AB blood type can contribute either an A or a B allele to his offspring. The heterozygous woman has one A allele and one unknown allele, which could be either A or O. If the woman contributes an A allele, the child will have either blood type A or AB. If the woman contributes an O allele, the child will have blood type O.
Since the woman is heterozygous for blood type A, there is a 50% chance that she will contribute an O allele. Therefore, 50% of their offspring would have blood type O.