xg antigen system xg antigen system the xg antigen is a red blood cell surface antigen discovered in 1962. by researchers at the mrc blood group unit. xg blood groupinterpretation of antibody panel to detect patient antibodies towards the most relevant human blood group systems, including xg. further information: blood compatibility testingidentifierssymbolxgalt. symbolspbdxncbi gene7499hgnc12806refseqnm_175569other datalocuschr. x p22.32 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. frequency population frequencies of xa population samplen 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