Biochemistry of ABO Antigens

The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes.
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, IA, and IB. 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).
Source : https://en.wikipedia.org/wiki/ABO_blo...