I am no expert on evolution or genetics either, but there are genetic diseases that skip generations or even more generations, still the genes are in the persons as I've understood. Perhaps the same is the case with homosexuality, maybe we all have that particular gene that might cause it, but is it less developped in most of us.
I'm just guessing here, as I don't have a definite answer.
Perhaps homosexuality is evolution's way to save us from overpopulation
