Eye Color Explained

Now that we have the human genome sequenced, it should be simple to determine someone's eye color just by analyzing their DNA, right? Turns out, not so much.

University of Queensland geneticist Rick Sturm suggests that the genetics are not so clear. “There is no single gene for eye color,” he says, “but the biggest effect is the OCA2 gene.” This gene, which controls the amount of melanin pigment produced, accounts for about 74 percent of the total variation in people’s eye color.

Sturm has recently shown that the OCA2 gene itself is influenced by other genetic components. After gene-typing about 3,000 people, Sturm found that how OCA2 is expressed—and how much pigment a person has—is strongly linked to three single nucleotide polymorphisms (SNPs), or single letter variations, in a DNA sequence near the OCA2 gene. That suggests a more complicated story than the blue-recessive/brown-dominant model of eye color. “For example, among individuals carrying the SNP sequence “TGT” at all three locations on both copies of the gene, 62 percent were blue-eyed,” says Sturm’s colleague David Duffy. By contrast, only 21 percent of individuals carrying only one TGT copy at each location and 7.5 percent of those lacking the TGT entirely had blue eyes.

Depending on the particular combination of SNPs inherited, a person can have a range of OCA2 activity that lands them on the spectrum between blue and brown eyes. What about green eyes? “Green eyes probably represent the interaction of multiple variants within the OCA2 and in other genes, including perhaps the red-hair gene,” Duffy says.

This is good news for you Caucasians criminals, for while the CSI team can determine race from DNA left at a crime scene, it is going to be a while before they can also test for eye color. Bad news on the other hand for those of you who want a designer baby, as what is the point if you can't even choose your baby's eye color?

via Discover Magazine