The XG antigen is a red blood cell surface antigen discovered in 1962 by researchers at the MRC Blood Group Unit.Mann, J. D., Cahan, A., Gelb, A. G., Fisher, N., Hamper, J., Tippett, P., Sanger, R., Race, R. R A sex-linked blood group. Lancet. 1962;279:8.
The PBDX gene that encodes the antigen is located on the short arm of the X chromosome. Since males normally have one X chromosome they are considered hemizygotes. Since women have two copies of the gene and could be heterozygotic for the presence or absence of the functioning gene they could (through the process of lyonisation) express the functioning protein on just some of their red blood cells.
Clinical diagnostic Clinical testing in patient care for Xg antigens follows published minimum quality and operational requirements, similar to red cell genotyping for any of the other recognized blood group systems. Molecular analysis can identify gene variants (alleles) that may affect Xg antigens expression on the red cell membrane.
Frequency Population frequencies of XaHarrison et al. (1977): Human biology – An introduction to human evolution, variation, growth and ecology. Oxford University Press, Oxford, . Population SampleN Xg%Australian Aborigines35279Chinese, mainland17160North Europeans5,38866Indians, Bombay10065Israelis20166American Indians30877New-Guineans26385New York's Afro-Americans21955Sardinians32276Taiwan Chinese17853Taiwan Aborigines16438
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