Weegy: In the ABO system, A and B are codominant, and O is recessive. Thus, if a person's ABO blood type is O, he or she has two O blood types. If, however, a person's blood type is A, he or she has either two A or one A and one O. [ Similarly, if a person has type B blood, this indicates the presence of either two B's or one B and one O. Finally, some people have type AB blood, which means they inherited both an A and a B.