I think it is not just one gene that is transferred from parent to child. Rather it is a gene that is being expressed that is usually isn't suppose to be (no offense to gays, 90% of the population are straight, thus the norm).

Also I read somewhere that gays help with population control. If the population is too great then there is a chance that resources will diminish to the point the population suffers and starts to die off. So have a few gays in the mix will help slow population growth.