Homosexuality is now widely being seen as a biological component, not a choice as it once was thought of. Homosexuality does seem to have a genetic component and the gene could possibly be hereditary. The studies being down are tryng to better understand this. There is no conclusive evidence yet, but at least we're looking.
If we assume approximately 2% with same-sex attraction in the general population, and the distribution is totally random, it is rather amazing (to me) that more than 2% of SSA siblings would also be SSA.
The problem is that same-sex attraction cannot be objectively observed as easily as you might observe eye color or earlobe size. Furthermore, if sexual orientation comes in three settings (same-sex, bi-sexual, and opposite-sex) then there is a chance that bi-sexual twins would diverge based on external influences. It is also likely (given the hostile attitude of society toward homosexuals in past years) many individuals with SSA convinced themselves that they were heterosexual in order to conform to society's conventions.
I could say "yes" except I can tell the yes side means to imply it's entirely genetic. The studies show identical twins are 52% of the time the same sexual orientation. But that still leaves 48%. That means there are other factors at work besides genetics. That does not mean it's a choice. That does not mean choice has nothing to do with it. Choice or rather the attempt to change could be a factor in some cases, there's room for that. But even if it was that wouldn't mean everybody can change if they want to.
Eight studies compiled over two decades regarding twins and homosexuality prove genetics is a "minor factor" in homosexuality and gender identity. In other words, one twin who was gay didn't necessarily mean his or her twin showed the same tendencies. If anything, homosexuality is a choice and isn't genetic. Either way, being gay isn't bad--you can't help who you fall in love with.