Abo blood group
According to the type of antigen present, a person may be assigned a blood type of a, B, ab or O. a second type of antigen, the rh factor, renders a positive or negative blood type. The abo blood group system is important because it determines who can donate blood to or accept blood from whom.
And since ab blood already produces both antigens, people who are type AB can accept any of the other blood types without suffering an immune Reaction. Classification of blood types in humans, a, B, ab and O. Blood transfusions of blood type O are suitable to transfer to all other blood groups. Blood groups tend to change in proportion in differing races, usually as a result of the geographical location in which the group has previously existed and consequently the ancestors who had such a blood group.