Well, that's the point - any "gay gene" mutation would be exceedingly rare, as it strikes right at the heart of what makes natural selection work - reproduction. Some homosexuals may have children... not a heck of a lot of them, though, and certainly not enough to represent 1% of the population. The very nature of such a gene would cause it to be on the losing end of the natural selection process.
Ah, but in the past there were strong social pressures for having children and wives, even if homosexual. That's changing now, and I suspect that, should homosexuality come to be more socially accepted, there will be FEWER homosexuals over time as homosexuals simply refused to pretend to be heterosexual by having wives and children.