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One of the most firmly established series of multiple alleles in humans involves the genetic locus controlling the blood types: A,B,AB and O. The ABO locus has three common alleles: IA, IB and IO. IAand IB are codominant (IAIB heterozygotes have both A and B antigens on their red blood cells) and IO is recessive (IO IO homozygotes have no ABO antigens on their red blood cells; IAIO andIBIO heterozygotes have A and B antigens, respectively, on their red blood cells).
The ABO locus controls the type of glycolipids found on the surface of erythrocytes, apparently by specifying the type of glycosyl-transferases (enzymes catalyzing the synthesis of polysacchrides) synthesized in the red blood cells. The specific types of glycolipids on the red cell surface provide the antigenic determinants that react with specific antibodies present in the blood serum. Reciprocal antibodies have also been identified in the serum of ndividuals.
The Rh factor discovered by Landsteiner in 1940 is based on presence of Rh antigen on RBCs. Rh negative mother (recessive) is immunized with Rh positive fetuses (dominant) during child birth. This creates problems during second childbirth when same mother (now containing antiRh antibodies due to previous childbirth exposure) delivers next Rh positive baby. AntiRh antibodies transferred from mother to second child at childbirth leads to lyses of child’s Rh positive RBCs, thus producing a disease called Erythroblastosis foetalis.
Blood transfusion compatibility for ABO blood group
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Blood group
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Antigen sugar
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Antibody
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Agglutinated RBC antigens
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Recipient blood groups
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A
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A, galactosamine
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Anti-B
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B, AB
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A or O
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B
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B galactose
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Anti-A
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A, AB
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B or O
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AB
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A, galactosamine B galactose
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None
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None
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A,B,AB or O
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O
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None
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Anti-A & Anti-B
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A, B, AB
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O
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Participants