Question: How do our genes determine wether we are homosexual or not?

Darren Logan answered on 9 Mar 2012:

I’m afraid we don’t have the answer to that yet, other than “its complicated”!

Some studies have shown that if one twin is homosexual, the other twin is more likely to be homosexual if they are identical twins than if they are non identical twins. This tells us there must be some genes that are involved, because identical twins have the same genes, while non-identical twins only share some of them.
But if it was only down to the genes, then whenever one identical twin was homosexual the other would be too, every single time. That does not happen, so we know that there must also be environmetal influences (such as how your brain develops while you are in your mother’s womb and in your first few years of life) that influence sexuality too.

That all said: I was involved in a study a few years ago that found a single gene in mice that, when missing, caused male mice to become bisexual. The gene is called TRPC2, and it needed for male mice to sniff out the difference between males and females. When it is missing, the mice get confused and try to mate with both sexes. However, humans do not have the part of the nose where this gene is found in mice, so it is definately not involved in human sexuality!