Archive for the 'Genetics' Category

One of my coworkers is expecting a child later this year and we got to talking about what color her child’s eyes would be. Nobody could remember the rules of eye color inheritance, so here’s the answer for my co-worker and others interested.

For starters, it’s quite complex. There are three genes called EYCL1, EYCL2, and EYCL3 that play a large role in determining the three main phenotypes brown, green, and blue. (Phenotype is a descriptive term used to define the manifestation of genetic and environmental factors.) These three phenotypes combine to make the six main eye colors: blue, grey, yellow, hazel, light brown, and dark brown.

There are also a number of SNPs (single nucleotide polymorphisms, pronounced “snips” that regulate the main genes. SNPs are changes in one single nucleotide letter of the DNA that affect gene expression.

These SNPs are located near genes for responsible for all sort of traits like eye and hair colors. For example, a recent study a few months ago talked about SNPs near the OCA2 gene that had effects on eye color. As the paper’s author Dr. Richard Strum told the BBC, “to use an analogy, one of the changes is like switching the light on and off, while the other is like changing the light bulb from brown to green.”

All these genes and SNPs come together to determine eye by regulating the amount of pigment produced. The main pigment in human eyes is called eumelanin. Brown eyes (the most dominate eye color in the world) contain high amounts of brown colored eumelanin. Another pigment that plays a role is the yellow colored lipofuscin.

Here’s a breakdown of eye colors and pigments:
Brown – high amounts of eumelanin
Amber or yellow – lipofuscin
Blue – a little yellow and little to none brown
Green – a lot of yellow and some brown
Hazel eyes – a combination of eye pigments that change with the amount of sunlight and clothing.
Gray – little to none of both yellow and brown
Albino eyes – gray is the color of eyes in people with complete albinism. The red eye feature that many people associate with albinos is due to the blood vessels that add a red tint. This tint can easily be augmented in the photographs because of the red eye effect.

As you can see, eye color genetics is far from straightforward. While eye color tends to run in families, it’s not unheard of two brown-eyed parents to have a blue-eyed child. To answer the original question that my expecting co-worker has: I found an interesting website that will take a shot at predicting the eye color of your future child. It’s called “What Color Eyes Would Your Children Have?”. I doubt they updated their formula for the recent discovery of the SNPs near the OCA2 gene (plus you would probably need to upload maternal and paternal DNA sequences for the SNPs), but it’s still an interesting little web application that will give you some decent odds.

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Posted by Tim Roth, author of the political blog Think Anew and Act Anew

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Sources:
1. Sturm R.A. and Frudakis T.N. “Eye color: portals into pigmentation genes and ancestry.” Trends Genet. 2004 Aug;20(8):327-32. PMID: 15262401. PDF Link
2. “Genetics of eye colour unlocked”, Paul Rincon, Science reporter, BBC News
3. “Eye color”, Wikipedia entry
4. “What Color Eyes Would Your Children Have”