Xq28

[3] The 1993 study by Hamer et al. 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.

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 in that small sample.

[3] A follow-up study, Hu et al. (1995), conducted by the Hamer lab in collaboration with two groups of statistical experts in 1995, corroborated the original results for males with homosexual brothers sharing Xq28 at significantly elevated rates.

[10][11][12] An official inquiry launched by the Office of Research Integrity (ORI) to investigate the allegations of selective presentation of the data ended in December 1996.

[13][note 3] In 2012, a large, comprehensive genome-wide linkage study of male sexual orientation was conducted by several independent groups of researchers.

[16] The study population included 409 independent pairs of gay brothers from 384 families, who were analyzed with over 300,000 single-nucleotide polymorphism markers.

The authors concluded that "our findings, taken in context with previous work, suggest that genetic variation in each of these regions contributes to development of the important psychological trait of male sexual orientation."

[21] Mutations involving the production of extra copies of the MECP2 and IRAK1 genes within Xq28 have been associated with phenotypes including anxiety and autism in mice.