The blood group system particular to primates that denotes the presence or absence of A,B, and O antigens on erythrocytes (red blood cells). The ABO gene encodes an enzyme responsible for producing A or B antigens, or an inactive enzyme resulting in the presences of O antigens. It is theorized that ABO and other blood groups provide protective diversity within populations to combat microbial invasion and has been maintained for millions of years. In humans, ABO is the major blood group for determining transfusion compatibility.
ABO blood groups