A man with blood type A and a woman with blood type B have three children: a daughter with type B, and two sons, one with type AB and one with type O. What are the genotypes of the parents? Solution Answer: Human blood group is determined by multiple allele system, in which IA and IB are co-dominant to each other and dominant over IO. In the given problem, the possible genotype of father is IAIO and the possible genotype of the mother is, IBIO. This is because they had children of AB blood group and O blood group. IAIO* IBIO -à IAIO (1/4, blood group A), IAIB (1/4, blood group AB), IBIO (1/4, blood group B), IOIO (1/4, blood group O)..