Xg antigen system explained

Xg blood group
Width:	370
Hgncid:	12806
Symbol:	XG
Altsymbols:	PBDX
Entrezgene:	7499
Refseq:	NM_175569
Chromosome:	X
Arm:	p
Band:	22.32

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.

Frequency

align=center colspan=7	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

Notes and References

Tippett P, Ellis NA . The Xg blood group system: a review . Transfus Med Rev . 12 . 4 . 233–57 . October 1998 . 9798268 . 10.1016/S0887-7963(98)80001-1.
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.
Ellis NA, Tippett P, Petty A, etal . PBDX is the XG blood group gene . Nat. Genet. . 8 . 3 . 285–90 . November 1994 . 7533029 . 10.1038/ng1194-285. 36695727 .
LINDSTEN J, FRACCARO M, POLANI PE, HAMERTON JL, SANGER R, RACE RR . Evidence that the Xg blood group genes are on the short arm of the X chromosome . Nature . 197 . 4868. 648–9 . February 1963 . 13930842 . 10.1038/197648a0. 1963Natur.197..648L . 4209911 .
Harrison et al. (1977): Human biology – An introduction to human evolution, variation, growth and ecology. Oxford University Press, Oxford, .