I know several people who are gay and what's very interesting is most of the people I know, is there are people in their family, sisters/brothers/uncles/etc. That are also homosexuals. I suspect there might not be "one gene" that makes a person a homosexual, but a collection of genes that increase the odds of someone being homosexual.
That being said, I feel like search for such a gene is to combat religious beliefs that homosexuality is wrong.
I'm still confused with why so many people are obsessed with the sexual orientation of another person?
I remember one time, I attended a meetup that was focused on LGBT startups. In the elevator, there were four people; two other men, a woman and me.
One guy who was apparently by himself and didn't read the agenda of the meetup asked the "couple" next to him how difficult it was to start a company and be in a relationship. The man replied "We're not a couple, I'm gay." then the women laughed and said, "I'm also gay, and this meetup is the LGBT community raising capital for their company."
The guy then turned to me and asked: "Are you also gay?" I replied: "No, but that headband you're wearing might be." Everyone but he laughed, and I thought that would ease the mood. This guy seemed very concerned about being a straight man in a gay meetup. I told him to relax and explained I was there to join a couple of friends who were speaking at the meetup.
I understand that some people feel uncomfortable being around people they are not used to being around; sexual orientation, race, income status, etc. They just haven't had that experience. Hopefully, that guy was able to feel more comfortable around none heterosexuals. They make amazing wing men and women :)