It's not genetic, it's hormonal ?
The registry testing of identical twins listed in post #3 indicate that it's highly unlikely sexual preference is determined in utero.
"Most stories about homosexuals I've read have them saying that at a very young age they felt different from people of their own sex."
It's probably fair to say that in those formative years ALL kids have moments of feeling "different" or not belonging. What seems to be lacking is parental involvement and particularly from the fathers.
Explain to me effeminate male homos and mannish female homos.