Xg antigen system

Xg blood group
Identifiers
Symbol	XG
Alt. symbols	PBDX
Entrez	7499
HUGO	12806
RefSeq	NM_175569
Other data
Locus	Chr. 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 X^a[5]
Population	Sample N	Xg %
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

Footnotes

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.