Actually, current research suggests that there is more than one "gay" gene.
The current theory is that these genes give various advantages to the bearers, such as better empathy, for example, and that only the agglomeration of many of these "gay" genes makes a person "gay". There is also reason to believe that it is down to the endocrimal amniotic mixture whilst the embryo is interuterine, and specifically the testosterone concentrations at various critical (and not yet determined) stages of early development.
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I would really like to see a reference for this.
The National Association for Resarch and Therapy of Homosexuality pretty much says otherwise
There was a study that showed a slightly less than 50% correlation between twins both being homosexual, but two other geneticists analyzed the data and claimed it was more support for environment than inheritance.