There are two possible blood types for children born to parents with blood types O and AB, type A and type B respectively. The child’s blood type is determined by the genes that determine blood type in both parents, i.e., blood type is genetically inherited. The combination of genes that can be used to denote blood type O by ii provides the i gene to the child, while the combination of genes that can be used to denote blood type AB by AB provides the A gene or the B gene to the child. Therefore, there are two possible combinations of blood type genes for children born to parents with blood type O and AB, i.e., Ai and Bi. If the combination of genes is Ai, the red blood cell membrane expresses the A antigen, i.e., the child has blood type A; if the combination of genes is Bi, the red blood cell membrane expresses the B antigen, i.e., the child has blood type B.