There is no SOLID evidence that claims homosexuality is genetic. Many of the claims are just hypothetical ideas that scientists cannot completely explain. So when I say that being homosexual is a choice, I mean that it cannot be biological. It's absurd to not think its a choice since some people do actually choose to be gay.
It is my opinion that being gay is ultimately a choice that people make. While I do believe in the notion that there is some predisposition to being gay, the choice of following through or rejecting homosexual behavior lies with each man and woman. Being gay is defined by the act, and not by the label.
No one chooses to be a heterosexual, so why would one assume that it is a choice to be anything else. You don't choose to be anything, otherwise we would have a lot more bisexuals on the planet. It more than likely has something to do with the pregnancy and their environment, and very little to do with choice or genetic predisposition.
When people say that being gay is a choice, I like to ask them when it was they chose to be straight. They usually stutter and sputter for a bit, then change the subject. You can not change or decide your sexual orientation. You get what you're born with, and that's it.
I honestly believe the being gay is not a choice. If being gay was a choice, then a straight man or woman could choose to be gay for a while and then go back to being straight right after to prove this point. No straight man would "go gay" just to prove that being gay is a choice. I believe that something inside a person is the reason for their sexual preference and that they cannot help the way they feel.
A lot of people do not seem to realize that homosexuality has been observed in at least 150 species of mammals. It is not just a human thing. Our closest relatives, the chimpanzee and bonobo, have been observed in homosexual acts. Every gay person I have ever spoken to knew they were gay from a young age, as well; far before puberty.
Being a heterosexual person myself I have no way to know the answer of this question from a personal viewpoint. My understanding of this situation from those that do identify as homosexual is that it is not a choice. They didn't simply decide one day to be gay, they feel they were born that way.