This guy thinks that because there is no gay gene, being gay is a choice. By that logic, there is no straight gene either. So us straight folks apparently choose as well. Not that any of this has anything to do with whether two committed adults love each other and should have equal protection under the law.
Though he's correct about the gene not being identified yet (nor is there one for straight people), there does seem to be a little bit of science indicating genetic and biological factors in determining your sexual orientation. Like, I dunno, lesbians and straight men have the same size brain hemispheres, as so do straight women and gay men; the more older brothers you have, the more likely you'll be gay; lesbians have longer ring fingers; there are startle response differences; gay people tend to be left handed more often; gay men have better memories than straight men; gay men's hair generally rotates differently (seriously); and many, many more!
All of this is irrelevant to the fact his argument has no bearing on a person's right to equality. Share so he knows you care.