Parents are blood types O and AB, and their children may have blood type A or B. The ABO blood group is a common clinical blood grouping system and is based on the surface antigen of red blood cells. One parent has blood type O with surface antigen OO and one parent has blood type AB with surface antigens A antigen and B antigen. The child’s blood type is controlled by both parents. The child has one chromosome from the mother and one chromosome from the father, so the child’s genes may be AO or BO. Because the A and B genes are dominant, and the O gene is recessive, the child’s blood type may be either A or B blood. Therefore, when parents’ blood type is O and AB, the child’s blood type may be A or B. However, the specific result should be based on the final test conducted by professional medical institutions.