Xq28

Xq28 is a genetic marker on the X chromosome found by Dean Hamer and others in 1993. Hamer's study led to his belief that they found a link between the Xq28 marker and male homosexuality, but the original study's results have been disputed.

1993 study
The 1993 study by Hamer examined 114 families of gay men in Italy and found increased rates of homosexuality among maternal uncles and cousins, but not among paternal relatives. Genetic linkage was studied in 40 of the families, in which there were two gay brothers. A correlation to Xq28 and other microsatellite markers was found in approximately 64% of the cases. A similar study by the same team conducted in 1995, again based on Italian material corroborated these results, but failed to find a link to the Xq28 gene among homosexual females. Although disputed animal trial have discovered removing of a certain gene appears to reverse homosexual behaviors. A group of Korean geneticists has altered the sexual preferences of female mice by removing a single gene linked to reproductive behavior. Without the gene, the mice gravitated toward mice of the same sex. Those mice who retained the gene, called FucM, were attracted to male mice. (FucM is short for fucose mutarotase.)

1999 study
A further study of these results in 1999 disputed the results. Studying Canadian material consisting of 52 pairs of gay brothers, George Rice and others found no statistically significant linkage in alleles and haplotypes and concluded against an X-linked male homosexuality gene.

When the refuting study was published in Science, Hamer disputed it, standing by his original results.