Saturday, August 15, 2009

Why so blue?

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"The eyes are the windows….of your face," says Christopher Walken in a hilarious SNL sketch about a man who puts googly-eyes on plants. Pretty windows, at that, in all those different colours…and it makes me think, just how is eye colour determined? It is a common misconception that eye colour is linked to just one gene, but as is the case with most biological phenomena, the matter is much more

For example, it was widely thought that blue eye colour is a simple recessive trait, meaning two blue-eyed parents would always produce a blue-eyed child. This caused a few paranoid moments during high school biology class, I'm sure. It has now believed that almost any parent-child colour combination can occur.

This is because eye colour is a polygenic trait, meaning it is the result of more than one gene interacting. There have been at least three genes found related to eye colour, and they all help control the type, amount and distribution of pigment in the iris. The iris also has different layers that vary in the type and level of pigment, creating even more possibilities. Did you know that in addition to brown, blue and green, eyes can be amber, violet, or even red? Or that eyes can contain spots, or even star patterns?

Heterochromia can produce two different coloured eyes, or large regions within one eye that are a different colour. This can be inherited or acquired from injury - a blood spot in the iris can permanently change the colour in that region.

People can even be born without an iris, in a creepy condition known as aniridia.

Of course, almost any eye colour is now possible with the invention of coloured contacts…window dressing at its most vain. It makes one wonder, when will googly-eyed contacts hit the market?

~Rheanna Sand

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