Your original post does not talk about heritability. So my answer was: heritability. But then I noticed that it was in the post title and I was confused and did not change my answer.

I posted a calculation on SSC. Let’s say that there is a mutation that is spontaneously created in 1 in 10,000, that it has a 10% chance of producing a homosexual phenotype and that the phenotype has 0.9 fitness, that is, yields an average of 1.8 children. Then the fitness of the gene in 0.99. So in equilibrium, the gene only reproduces itself 99%, so the remaining 1% must be made up by the spontaneous mutation. That is, the prevalence is 100x the spontaneous mutation rate. The prevalence is 1% of the population, of which 0.99% inherit the gene and 0.01% spontaneously acquire it. That’s a genotypic prevalence of 1%. The phenotypic prevalence is 0.1%.

I think 1 in 10,000 is the standard rule of thumb mutation rate. For example, achondroplasia (dwarfism) has a spontaneous mutation rate of 3 in 100,000 and an inherited rate of 1 in 100,000. Apparently dwarfs have about 1/4 of replacement fertility. (The fatality of homozygous achondroplasia complicates the situation. The gene definitely has a fitness of 1/4, but if dwarfs only marry dwarfs, the fitness of the people would be 3/8, I think.)

Also, the approach to equilibrium is exponential with base the fitness.