A new Scientific Reports study looking into the links between homosexuality in men and their genes has made a fascinating discovery: Two regions on two chromosomes do indeed seem to be different in gay men compared to heterosexual men.
It’s known that, for men, sexual orientation is partly based on the genes you inherit. Yes, it’s more complicated than that, but this is an unequivocal fact. The authors of the new study – led by geneticists and psychiatrists from the NorthShore University HealthSystem Research Institute – point this out early on.
“Male sexual orientation is moderately heritable (30 to 40 percent), but is multifactorial, with evidence of multiple genetic and environmental contributions,” they explain.
In the last three decades, it’s emerged that genetic variations do seem to have an influence over whether a man is homosexual or heterosexual. This new study sought to build on this evidence, and appears to have succeeded.
Using 1,077 self-identified homosexual and 1,231 self-identified heterosexual men of primarily European descent, they conducted a genome-wide association study, or a GWAS. This means they looked for differences in the genetic constituents of their subjects across their entire genome.
Ultimately, they managed to find two genetic regions that differed between the two populations. These regions were located on two different chromosomes, which are the thread-like structures that carry our genes.
One region is linked to a gene named SLITRK6, and can be found on chromosome 13; the other region is associated with a gene called TSHR, and was identified on chromosome 14. Variants of these genes appear to influence whether or not a man is homosexual.
Just having these variants doesn't mean the person will always be gay, by the way. There are certainly other genetic and external factors that influence this too.
The researchers note that “SLITRK6 is expressed especially in the diencephalon,” a segment of the brain that occurs very early on during embryonic development. Interestingly, the team point out that the diencephalon “contains a region previously reported as differing in size in men by sexual orientation.”
TSHR has a variety of associations, including with the hippocampus, the part of the brain that consolidates short-term memories into long-term ones. More importantly, this gene is linked to the behavior of the thyroid gland.