The ABO blood type is controlled by a single locus, called I, and the human population harbors three alleles: IA, IB, and i, which are often called A, B, and O, respectively. Each individual, of course (being diploid), only carries two copies of the gene. The relationship between genotype and phenotype is complicated. A is dominant to O, B is also dominant to O, and A and B are codominant, which means that the effect of both can be seen in the heterozygote (phenotype = AB). Possible phenotypes (= "blood types") are thus A (due to genotypes AA and AO, i.e. the same as symbolized by IAIA and IAi, respectively), B (BB and BO, i.e. IBIB and IBi), AB (AB, i.e. IAIB) and O (OO, i.e. ii).
a. Suppose that parents know their phenotypes, but not their genotypes: the father is type AB and the mother is type O. What are the genotypes of these parents?
b. What are all the possible blood type phenotypes among their children?