Position 1: Homosexuality is a chosen "lifestyle," like vegetarianism.

Position 2: Homosexuality is a disease, like schizophrenia.

Position 3: Homosexuality is a biological orientation, like left-handedness, and is neither chosen nor pathological.

Pat Robertson often claims that "obviously" there could not be a gay gene because nature only selects for genes that "increase reproduction." Robertson knows nothing about the subject. Any first-year college genetics student could point out that anti-reproductive traits are selected for all the time. How? Through something called "pleiotropy," the fact that genes have side effects, as do drugs. Nature not only could easily select for a gay gene, but it can, and does, regularly select for genes that *kill us. One example: the gene that nature selects to protect us from malaria. This gene has a devastating pleiotropic side effect-it's called sickle-cell anemia. If it turns out that the "gay gene" is simply another example of pleiotropy, this would suggest that homosexuality is, like sickle-cell disease, nothing more than a biochemical fluke. Why, then, should conservatives cower before the idea of a gay gene? Huntington's disease is caused by a gene, and that makes Huntington's neither "good" nor "acceptable."

A pretty good discussion in the link.