If child X has type A blood and father Y has type AB blood, what are the child's possible genotypes?

AA, AO

Explanation:

Blood type is one of the traits we inherit from our parents. There are three different alleles that determine it: A, B, and O. Their combination can produce four different blood types: A, B, AB, and O.

If a person has blood type A, their genotype is either AA or AO. The child's exact genotype will depend on the mother's, which we are not provided with. Her blood group is either A, O, or AB. The child definitely inherited one A allele from its father, and the second allele (A or O) had to be inherited from the mother. Her genotype can be AA, AO, AB, or OO. What matters is that her genotype contains one A or one O allele. That is how we can get a child with the AA or AO genotype if its father has the AB genotype.