Homosexuality is genetic. It has something to do with hormones and how the brain responds to stimuli that produces arousal. This trait can be passed on. Although straight people also engage in homosexual behavior maybe out of curiosity. Sometimes it's a phase that one goes through when trying to learn about one's own sexual orientation. You know 'experimenting' while developing the id, ego and super-ego of the mind.
Autism, OCD, and other psychological disorders are anomalies or conditions associated with disabilities that disrupts normal mental functions. Being gay doesn't make one mentally handicapped. There is no medication for homosexuality that makes them attracted to the opposite sex. Gays aren't placed in special ed classes like how children are with mental disorders.
It is a trait that others consider abnormal. But it's more social and personality problem than anything. Perhaps it started out as a deviant behavior. But it has evolved into being a normal trait. It's in all cultures. There are even gods and goddesses that were homosexuals. lol
I always understood that during pregnancy the woman get's stressed beyond the point of caring anymore. Stress-hormone levels drop accordingly particularly during the phase where the traits are established.
Usually it is environment, like an abusive or overbearing husband that sets the switch of. The point is that any and every couple can have a kid that has a greater same sex like or arousal.
When the conditions are right that is. Culture has nothing to with it. But we will find that f.i. after wars the number of kids born with this preference is higher.
Furthermore homosexuality or other rare behaviours, though hard wired in the individual are fringe genetic occurances.
But there is always room at the edge so to say.