There are lots of straight-acting closeted gay parents.
This is not really an answerable question, because human sexual desire covers such a broad spectrum, and sexual BEHAVIOR an even broader one, sometimes not really guided by carnal desire at all. Then take something as complicated as that and add centuries of cultural norms and taboos worldwide, and back through to antiquity.
People can have primary desires, and root that as a major anchor for their identity. But there's never been a gene found that causes being gay, as 21st century Americans understand the conceit to mean, nor will one ever be found.
"Don't think it hasn't been a little slice of Heaven just because it hasn't!" --Bugs Bunny