Xg antigen system

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Xg blood group
Alt. symbolsPBDX
Other data
LocusChr. X p22.32

The XG antigen is a red blood cell surface antigen discovered in 1962.[1] by researchers at the MRC Blood Group Unit.[2]

The PBDX gene that encodes the antigen is located on the short arm of the X chromosome.[3][4] 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.

Population frequencies of Xa[5]
Population Sample
Australian Aborigines 352 79
Chinese, mainland 171 60
North Europeans 5,388 66
Indians, Bombay 100 65
Israelis 201 66
American Indians 308 77
New-Guineans 263 85
New York's Afro-Americans 219 55
Sardinians 322 76
Taiwan Chinese 178 53
Taiwan Aborigines 164 38
Taiwan Chinese 178 53


  1. Tippett P, Ellis NA (October 1998). "The Xg blood group system: a review". Transfus Med Rev. 12 (4): 233–57. doi:10.1016/S0887-7963(98)80001-1. PMID 9798268.
  2. 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.
  3. Ellis NA, Tippett P, Petty A, et al. (November 1994). "PBDX is the XG blood group gene". Nat. Genet. 8 (3): 285–90. doi:10.1038/ng1194-285. PMID 7533029.
  4. LINDSTEN J, FRACCARO M, POLANI PE, HAMERTON JL, SANGER R, RACE RR (February 1963). "Evidence that the Xg blood group genes are on the short arm of the X chromosome". Nature. 197 (4868): 648–9. doi:10.1038/197648a0. PMID 13930842.
  5. Harrison et al. (1977): Human biology – An introduction to human evolution, variation, growth and ecology. Oxford University Press, Oxford, ISBN 978-0-19-857165-0.