@ummmm
//My youngest son is gay.//
On one level, you could view that as contradicting any idea of a 'gay gene' necause his siblings are not that way inclined.
But it could be akim to the way that you need two copies of a gene to have blue eyes, or red/ginger hair and that can only happen when both parents are carriers.
But it could be way more complex than this. Did anyone see that Horizon programme, the other week, about whether we had male or female brains, regardless of our physical gender?
The genetic basis for how our brains are wired up and, hence, what our preferences end up becoming could entail hundreds of genes. That would make inheritance of the trait so complex as to require studying large numbers of families. All highly intrusive and unlikely to happen.
If I have a stance it is only that the children seem to have no choice over who brings them up. What if sex-Ed teaches them about homosexuality first and that is when they twig that other kids families do not consist of two women? Will it make them feel self-conscious and/or "abnormal"?