Human blood types show both codominance and multiple alleles. The blood types are A, B, AB, and O. The alleles for A, B, and O are IA, IB, and i respectively. A and B are codominant, and O is recessive.
One parent is blood type AB and the other is B. The children are one-fourth A, one-fourth AB and one-half B. Determine the genotypes of the parents.