If one out of ten people are gay, how many people carry the "gay gene"?

I don't think (hope) she made-up this question herself, but it is sort of a heredity (p/q) and probability question. I am much more comfortable with the latter.

This question however, is unsolvable. Based on assumption 1, the couples are all straight. The only way to get a gay girl (based on the other assumptions you have outlined) is if she gets the gene from BOTH her mom and her dad. If the "gay gene" is carried only on the x chromosome, the only way the father can have it is if he IS gay himself. The daughter needs both (it's recessive), so the only one he has to give must carry it.

Using gay men and carrier women (no lesbians) I can give you an answer though.You are right. You would need at minimum 10 women and 5 (gay) men that have the gene. But it is unlikely that it would happen this way by chance. You must assume that if there are more non-carriers, then most carriers would get paired with non-carriers, which would alter the proportion of children that are gay.

I should also mention that if there are an equal number of gay fathers and female carriers, you would expect twice as many gay sons as daughters, since a carrier mother has a 50/50 chance of having a gay son, while a gay father can only have a gay daughter if the mother is a carrier as well. In other words a carrier or lesbian mother is needed to have gay children (based on your assumptions). This means there are more gay fathers than carrier mothers (in order for there to be the same number of lesbian daughters as gay sons). A little bit of work figuring-out the proportions of gay sons and daughters will eventually lead to the realization that in order for there to be the same number of gay sons and daughters, there must actually be 4 gay fathers for every female carrier (this was by working with MUCH smaller groups, I did a group of 4 men and 4 women and discovered this was the only way that males and females came-out equally likely to be gay). This next part will take a little to explain, so I hope you will be fine with my lack of work. We know that 10% of the children are gay. In order to get this percent, about 15.8 of the mothers are carriers and therefore 63.2 of then fathers are gay (16 and 64 would give you 10.24% of the children being gay, but would maintain an equal number of males and females). This is taking into account that not all of the carrier mothers will be paired with gay men and not all of the gay men will be paired with carrier mothers.

I hope you noticed that if you had asked this question seriously, at least one of these assumptions are likely incorrect. And if this was a serious question, it would not be equally split between boys and girls, there would be twice as many gay boys as gay girls. That would be roughly 6.67% of girls and 13.33% of boys. This would change the entire last part of my answer as well. But I doubt this is quite how it works.

This is probably in the wrong section of the forum thing.

Besides, it's a silly question.