Where did the first gay come from? I don't believe for one second that gays are genetically predisposed to be gays.
I do think it is choice (whether that be conscious or not) but not genetics.
I think that it is dependent upon hormone response, so probably linked to genetics in some way.
Homosexual activity is common among every species of mammal on the planet, so it may simply be a natural response to certain stimuli.
The issue gets confused by the 'choice' some make due to 'fashion trends' and lifestyle choices.