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There are four main blood groups defined by the ABO system: 1  blood group A has A antigens on the red blood cells with anti-B antibodies in the plasma. 2  blood group B has B antigens with anti-A antibodies in the plasma. 3  blood group O has no antigens, but both anti-A and anti-B antibodies in the plasma.ntroduction. There are four main blood groups (types of blood): A, B, AB and O. Your blood group is determined by the genes you inherit from your parents.
Within the ABO/Rhesus Group systems which are used to classify most blood types, there are several rare blood types. The rarest is AB-, with less than one percent of the world's population having this blood type.