Xq28

Xq28 is a chromosome band and genetic marker situated at the tip of the X chromosome which has been studied since at least 1980. The band contains three distinct regions, totaling about 8 Mb of genetic information. Xq28 contains the 12 genes of the melanoma-associated antigen (MAGE) family, of which MAGEA11 has been identified as a coregulator for the androgen receptor. Duplications of certain genes within Xq28, namely MECP2 and IRAK1, have been associated with phenotypes including anxiety and autism. The marker came to the public eye in 1993 when studies by Dean Hamer and others indicated a link between the Xq28 marker and male sexual orientation.

Hamer's 1993 and 1995 studies

The 1993 study by Hamer examined 114 families of gay men in the United States and found increased rates of homosexuality among maternal uncles and cousins, but not among paternal relatives. This pattern of inheritance suggested that there might be linked genes on the x-chromosome, since males always inherit their copy of the x-chromosome from their mothers. Polymorphisms of genetic markers of the x-chromosome were analyzed to see if a specific marker was shared by a disproportionate amount of brothers who were both gay. The results showed that among gay brothers, the concordance rate for markers from the Xq28 region were significantly greater than expected for random Mendelian segregation, indicating that a link did exist.