The father has blood type a and the mother has blood type b. The child may have blood type A, B, O, or AB. The child’s blood type is inherited from the parents’ blood genes, half from the father and half from the mother. Because there are three alleles, A and B. AB is the dominant gene and O is the negative gene. A father with blood type A gene may be AA or AO. has A antigen and may pass the A gene or OA gene to the child, and a mother with blood type b gene is BB or OB and has B antigen and may pass the B gene or O gene to the child. Therefore, with father’s blood type a and mother’s blood type b, the child could have all four blood types A, B, O, or AB, which means that any of all the blood types of the ABO blood group system could be present in the child.