Reference Work Entry

Encyclopedia of Genetics, Genomics, Proteomics and Informatics

pp 6-6


ABO Blood Group

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

ABO blood group

Blood Group (Frequency in Caucasoids*)


Antigens Formed

Antibodies Formed

Clumping With

Blood Type Acceptable for Transfusion


O (0.45)










A (0.44)

iAiA or iAiO






B (0.08)









AB (0.03)







*The frequency of these alleles varies in different populations. For the calculation of frequencies, see gene frequencies. Actually, the A type exists in A1 A2 forms; in about 1–2% of the A2 and 25% of the A2B individuals, anti-A1 antigens occur.

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 medicine in paternity suites, in typing bloodstains, semen and saliva in criminal cases. Immunologically active forms may be recovered in old human remains and can also be used in archeological research. This blood group provided some correlative information in cancer research, e.g., in O individuals afflicted with carcinomas A antigen may be detected in 10–20% of the cases. The major clinical characteristics are as follows.

It appears, changes in glycosyltransferase activity are not uncommon in several types of tumors. The frequency of the various ABO alleles varies a great deal in the world population. It has been shown that the O blood type provided some protection against the most severe form of syphilis (Treponema pallidum) but somewhat higher susceptibility to diarrhea caused by some viral and bacterial infections. The B blood group may have afforded some protection against smallpox, plague and cholera.

Universally compatible red blood cells can be obtained by two bacterial glycosidase gene families that provide enzymes capable of efficient removal of A and B antigens at neutral pH with low consumption of recombinant enzymes. The crystal structure of a member of the -N-acetylgalactosaminidase family reveals an unusual catalytic mechanism involving NAD+ (Liu QP et al 2007 Nature Biotechn 25:454). ABH antigen, Lewis blood group, blood groups, Treponema pallidum , forensic genetics; Race EE, Sanger R 1975 Blood groups in man, Blackwell, Oxford; Chester MA 2001 Transfus Med Rev 15:177; Patenaude SI et al 2002 Nature Struct Biol 9:685.

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