Xg antigen system

The XG antigen is a red blood cell surface antigen discovered in 1962.cite journal |author=Tippett P, Ellis NA |title=The Xg blood group system: a review |journal=Transfus Med Rev |volume=12 |issue=4 |pages=233–57 |year=1998 |month=October |pmid=9798268 |doi= |url=http://linkinghub.elsevier.com/retrieve/pii/S0887796398000017] Mann JJ, Cahan A, Gelb AG, et al. A sex-linked blood group. Lancet. 1962;i:8.]

The PBDX gene that encodes the antigen is located on the short arm of the X chromosome.cite journal |author=Ellis NA, Tippett P, Petty A, "et al" |title=PBDX is the XG blood group gene |journal=Nat. Genet. |volume=8 |issue=3 |pages=285–90 |year=1994 |month=November |pmid=7533029 |doi=10.1038/ng1194-285 |url=http://dx.doi.org/10.1038/ng1194-285] cite journal |author=LINDSTEN J, FRACCARO M, POLANI PE, HAMERTON JL, SANGER R, RACE RR |title=Evidence that the Xg blood group genes are on the short arm of the X chromosome |journal=Nature |volume=197 |issue= |pages=648–9 |year=1963 |month=February |pmid=13930842 |doi= |url=] 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 are absence of the functioning gene they could (through the process of lyonisation) express the functioning protein on just some of their red blood cells.

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