why your eyes are blue

I just found this abstract, which I’ve translated into Layman for you. Interesting stuff!

We have previously shown that just one gene accounts for 74%
of variation in human eye color. We looked harder to see what was going on with this gene and the inheritance of eye color and other pigmentary traits associated with skin cancer risk in white populations. We had 3,839 adolescent twins, their sibs, and parents to study, can you believe that? Yay, Australian twin registry [these authors are in Brisbane].

The best association for blue:non-blue eye color was found with a particular genetic variant, let’s call it TGT, which was the most common variant in the population, but which was in a region of the gene that nobody ever thought would be important. Guess we were wrong because the association was MAD HUGE. Like, 5 or 10 times stronger than the results all you people studying complex diseases have to deal with. We’re not gloating or anything though–keep it up guys, you’re doing great! Anyway, this is how strong this variant is: 90.5% of people with two copies of T-G-T had blue/gray or green/hazel eyes, the rest had brown eyes. TGT was also real common in people with light brown hair and in people with fair and medium skin types. People who didn’t have the second T of TGT were pretty much without freckles and had fewer moles too.

The strength of this result, over which we are still not gloating, suggests that the regions nobody thought were important are very important indeed, and y’all should take a better look at your samples. Oh wait! Your diseases are way too complicated! You can’t! Ah hah ha ha ha ha hahaha ahahahahaaaa.
(Funded by Australian and US government agencies.)

What gets me about this finding is how GATTACA it is. If you could pick your genotype at this particular place, you could engineer your kids to be far more likely to have any eye color you wanted (and if you knew about other sites that contributed you could be even surer). What’s more, with knowledge like this, you could futz with your own eye color with drugs or gene therapy.

While I hit my head against the wall figuring out the genetics of bipolar disorder — which, as a complex disease, will never see genes with this large an effect — someday these researchers will be able to walk down the street and see the literal fruits of their work, just by making eye contact. Oh, brave new world.