Xq28 is a chromosome band and genetic marker situated at the tip of the X chromosome which has been studied since at least The study by Hamer et al. This pattern of inheritance suggested that there might be linked genes on the X chromosomesince males always inherit their copy of the X chromosome from their mothers.
Polymorphisms of genetic markers of the X chromosome were analyzed for Chromosome xq28 homosexuality and christianity families 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 in that small sample.
It was concluded that at least one form of male homosexuality is preferentially transmitted through the maternal side and is genetically linked to the Xq28 region. A follow-up study, Hu et al. This study also included heterosexual brothers, who showed significantly less than expected sharing of the Xq28 region, as expected for a genetic locus that in one form is associated with same-sex attraction and in another form is associated with opposite-sex attraction.