Blood type represent contributions from both parents. A total of 36 human blood group systems and 346 antigens are now recognized by the International Society of Blood Transfusion (ISBT). The two most important ones are ABO and the Rh blood group systems; they determine someone's blood type (A, B, AB and O, with +, − or null denoting RhD status) for suitability in blood transfusion. A complete blood type would describe a full set of 30 substances on the surface of red blood cells, and an individual's blood type is one of many possible combinations of blood-group antigens. Across the 36 blood
ABO blood group system the precise glycosyl transferase set that confers the A, B and O epitopes. Blood groups are inherited from both parents. The ABO blood type is controlled by a single gene (the ABO gene) with three types of alleles inferred from classical genetics: "i", "I", and "I". The "I" designation stands for isoagglutinogen, another term for antigen. The gene encodes a glycosyltransferase—that is, an enzyme that modifies the carbohydrate content of the red blood cell antigens. The gene is located on the long arm of the ninth chromosome (9q34). The "I" allele gives type A, "I" gives type B, and "i"