ABO Blood Group

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Represented by three major types of alleles (human chromosome 9q34) displaying codominance (see Table A2).

These blood types are extremely important because inappropriate mixing (in blood transfusion) results in agglutination that prevents the flow of blood through the veins and oxygen transfer, and it is potentially lethal. These antigens are actually carbohydrates (attached to polypeptides), and the genes A and B specify α-d-N-acetylgalactosaminyltransferase and α-d-galactosyltransferase enzymes, respectively. Gene O is not active as an enzyme. The A and B enzymes (Mr about 100,000) are dimeric and structurally similar to each other. The A and B molecules are identified as A and B antigens. Occasionally maternal antibodies against the A and B antigens may enter, through the placenta, the fetal blood stream and affect adversely the erythrocytes causing anemia and hyperbilirubinemia. In such cases medical treatment may be required. The ABO system has also a limited use in forensic medic ...