How does your new genetics study compare to similar studies?
We have 400 pairs of gay brothers and almost 400 families. It’s three times as big as the next biggest study.
What is your study searching for and what are the main findings?
We are looking for a series of markers that show linkage on the various chromosomes. Probably the main thing is that the Xq28 [Dean Hamer’s genetic study] finding seems to be supported in a pretty large sample. And there probably is some gene or genes in that region contributing to variation of the trait.
What do identical twin studies show in terms of sexual orientation?
The twin studies have shown more similarity for the trait, between the identical twins that share all the same DNA. Compared to same-sex fraternal twins which, are just like any other brothers, born at different times in terms of the amount of DNA they share, which is about 50%. Both of those types of twin pairs share a lot of environment. So, when we find the identical twin pairs are more similar on the trait to the same sex fraternal twins that tells us that genetics is contributing a fair bit to the trait.
How big is the role genetics play in sexual orientation?
It’s not as high as a lot of conditions that are studied genetically. It is low to moderate heritability. There are different estimates. Maybe somewhere around thirty to forty percent of the variation.
Opponents of LGBT equality like to say, “There is no gay gene?” As a scientist who conducts genetic studies, what is you response?
When people say there is the “gay gene” it’s an oversimplification. We don’t think there is just one gene involved. There are a number of genes. We also don’t think genetics is the whole story. It’s not. And whatever genes contribute to sexual orientation, you can think of it contributing to heterosexuality as much as you can think of it contributing to homosexuality. It contributes to variation of a trait. So, it seems like there are a number of genes involved. And maybe we’ve got more of a little bit of a handle now that chromosome Xq28 seems to be replicated. Although, there are still quite a few genes in that region. So, there is more work to do to narrow things down.
Could this research lead to people having designer babies?
The result of this kind of research is not that we have a particular variant that has such high predictive power. And the reason is we are talking about complex genetic scenarios and statistical differences. We are not talking about all or none kinds of things. So we are not talking about, for example, the vast majority of the time we have the XY chromosome you are male. You have two X chromosomes you are female. It’s nothing at all like that level of prediction. And so I think that people who might even be thinking about, well am I going to try to have a designer baby, one of the words you hear used. This would not even be useful for that kind of thing even if someone had an aim to do that. It is certainly not our intention.