The blood group characteristic in humans is controlled by three set of alleles, namely, IA, IB, and i. The alleles, IA and IB, are equally dominant whereas allele, i, is recessive to the other alleles. The individuals with genotype, IA IA and IA i, have blood group A whereas the individuals with genotype, IB IB and IB i, have blood group B. The persons with genotype IA IB have blood group AB while those with blood group O have genotype ii.
Hence, if the father has blood group A and mother has blood group B, then the possible genotype of the parents will be
IA IA or IA i IB IB or IB i
A cross between homozygous parents will produce progeny with AB blood group.
A cross between heterozygous parents will produce progenies with AB blood group (IAIB) and O blood group (ii).