Question

A woman with the blood type B has a child with blood type O. What are the genotypes of the mother and child? Which genotypes could the father not have?

Answer 1

If the child exhibits an O phenotype, it means the child has two O alleles. One must have come from the mother; the other from the father. We know that the mother must be OB and the Dad can be either AO, BO or OO. He cannot be AB, AA or BB. Clear?