Here is evidence from brain studies about homosexuality. These show that
there are differences which most likely were present before birth. It also
details studies that show there is some genetic basis, but it is certainly
weaker than the genetic basis for say blue eyes. There is also a genetic
basis for dyslexia and ADD, but again it is not extremely strong. The
comment about there being no genetic basis is easily disproven by the cited
studies.
As to whether it is sometimes a choice, there is no resolution, but the
studies point to the fact that it is sometimes not a choice.