Science hasn’t searched. It may not be a gene at all. It certainly is an aberration. But the fact of the matter is that we have done little or no research in the are because of political correctness or fear. Fact is we simply on’t know and unless we get the politics out of it, we will never know..
Normally I ashamed to admit this, but one of my undergraduate majors was Psychology. I am aware of several failed attempts to clinically link homosexuality to genetics. And this was 20 years ago. As things stand right now in the medical community, the "born this way" argument is junk science.
By coincidence, my roommate who was as heterosexual as they come had an identical twin at my small school who was equally flaming.