Eye Color More Complex Than We Realized

Our genes determine everything from body type and facial features to hair and eye color. Experts once believed the genetics behind eye color was simple, with a small number of genes responsible for our many subtle differences. Now, they’re finding they’ve barely touched the surface.

There may be several dozen distinct gene variations that can come together in different ways to affect both the color and health of our eyes. We have details on the connections.

A Basic Understanding of Eye Color

Some of us might remember from high school biology class that four gene fragments, or alleles, determine eye color: B, b, G and g. According to popular belief, each parent contributes two alleles, and the configuration of the four is what ultimately decides eye color.

For example, any combination that contains B (Bbgg, BBGG, bBgG) results in brown eyes, whereas bbgg is the only combination that causes blue eyes. For green eyes to occur, G must be present, but B cannot. Using this knowledge, we can give a broad but simple prediction of a person’s eye color by looking at different variations of the above combinations — but keep in mind that the key words here are “broad” and “simple.”

Complex Gene Combinations and Eye Color

The issue becomes more complicated when we realize more than just a few genes contribute to these color differences. Previous research has uncovered at least 10 areas in our DNA that affect eye color. A study recently released in Science Advances suggests there may be dozens more, and a person’s eye color ultimately results from a complex lineup of genes. 

The underlying genetics become even more complex when it comes to the many varieties of hazel, amber and gray eye colors that exist. Whereas experts used to look at eyes in terms of three colors, brown, blue and green, they now count at least seven distinct eye color types. These differences are possible because many groups of complex genetic code dictate both the types of pigments in our eyes and also the amounts of each; small differences in either can affect the final color.

Here’s where the research becomes really interesting. Where someone of European descent with a particular combination of genes might have blue eyes, someone of Asian descent with a similar genetic combination might have light brown eyes. Even more, although these groups might present with different eye colors, they may still have overlaps in genes associated with certain pigment-related health conditions. More research into these genetic overlaps could help uncover the links behind several eye conditions and possibly offer new directions for treatment options.

The study of genetics is complicated, and we still have a lot to discover. Eye color, and the genes that contribute to it, could say a lot about a person’s background as well as their current and future eye health. There’s more to each of our eyes than whether that one group of genes is BBGG (brown eyes), bbGG (green eyes) or bbgg (blue eyes), and the results are literally as unique as our fingerprints.

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