What Makes Our Eyes Different Colors?
Ah, 1907. In many ways, it was a simpler time. It cost only a nickel to go to the movies, and people thought that a single gene determined eye color. That was the year that two researchers, Charles and Gertrude Davenport, proposed that a recessive gene was responsible for blue eye color. They said that blue-eyed parents always produced blue-eyed children. Case closed. Somehow they managed to ignore a couple of kids with hazel eyes in their data. Other scientists of the era said, “Uhmmm, wait a minute…” but the criticisms didn’t stick.
(By the way, 1907 also had a typhoid epidemic and a financial crisis. Just sayin’.)
This simplistic explanation of the genetics of eye color was taught for decades. For a lot of people, it was one of the most-remembered facts from science class, right up there with ROY G BIV.* Though ROY proved to be enduring, the explanation of eye color…not so much. Eye color is a lot more complicated than the Davenports believed.
(*Look it up.)
Eye color depends upon how much melanin is in the eye. (Whoops, getting a little off course here…) The substance is a pigment, and the amount of melanin in skin, hair, and eyes controls their colors. By the way –melanin is also found in the eye’s retina and is involved in vision. (OK, back on track.)
When it comes to eye color, a couple of genes on chromosome 15 appear to be the big shots. However, several other genes are involved to some extent, and the interaction among these genes is important, too. With versions of genes from both parents, a child may have access to more melanin that either parent had alone. When these genes build up the amount of melanin, some blue-eyed parents wind up with a surprise: a brown-eyed baby. So they can sing along with Van Morrison. *
(*Check out http://en.musicplayon.com/play?v=887074) **
(** If the stripes are too much, watch Bruce Springstein’s cover at http://wfgr.com/bruce-springsteen-covers-brown-eyed-girl-video/)***
(*** Let’s dedicate that song to the Davenports. They may not have been 100% on the mark, but scientific knowledge grows and expands from the early researchers.)