Where do green eyes come from? , page 1

reply to post by asmeone2

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Source

In all of this discussion, we’ve ignored green eyes. And all the colors in between. Do these results tell us anything about green eyes? A bit.

There are lots of possible theories we can come up with to explain green eyes. One idea is that OCA2 explains all eye color. The data in this paper (and all of the inheritance studies that have been done) do not support this model.

Why would people even consider this model? How could you get green eyes with just OCA2? By having it only partially on.

Remember, lots of melanin in the stroma of the iris gives brown eyes and little or no melanin here gives blue ones. Green eyes are thought to happen when there is an intermediate amount of melanin.

And genes aren’t only on or off. They are more like a dimmer switch on a light.

So green eyes might happen when OCA2 isn’t going at full strength. The findings from some early, smaller studies suggested that this might be the case. But this bigger study doesn’t really support this idea. So green eyes (and presumably all the other colors) probably come from other genes.

Also, on eyes changing color with age....Can eyes change color with age?

reply to post by Desert Dawg

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Not to nitpick but I mean grass green eyes--not hazel--which is really just light brown.

But I have noticed a lot of people who come from the area of Hungary or Romania that have the red hair/hazel eyes that you describe, maybe that is the aea of Europe your wife comes from?

It's facinating to me that most of the major European countries have a certain "look" to them.

Edit: I have no idea at all if animal eye/hair color is decided the same way as humans, if anything I think it would be more complex, since they have some additional eye colors and often display patterns of different hair color.

[edit on 5-10-2008 by asmeone2]

reply to post by asmeone2

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Pure green eyes are rather rare; I rarely see anyone with pure green eyes. Even mine....I have pure bottle green irises, but they are rimmed in a smoky blue. No yellow, no brown, but pure green with that smoky blue rim.

On my father's side of the family, all of our eyes changed colors. Him, his sister, my cousin, and me. But, their's went from hazel or blue to an almost colorless aqua. Mine went to the green.

It's odd....

Originally posted by skeptic1
reply to post by asmeone2

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Pure green eyes are rather rare; I rarely see anyone with pure green eyes. Even mine....I have pure bottle green irises, but they are rimmed in a smoky blue. No yellow, no brown, but pure green with that smoky blue rim.

I want to post a picture now. I have the "pure green" eyes in question, so does my family.

reply to post by asmeone2

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Probably in families, they can pass down, as long as they aren't over-run by the dominant gene (since brown seems to be dominant and blues are recessive).

Someone brought up Ireland earlier, and those folks have the greenest eyes imaginable. But, there has been much cultural interbreeding and that seems to have diluted cultural traits.

The Nordic culture with the pale skin, pure blonde hair, and ice blue eyes. Native American culture with deeper toned skin, brown eyes, and black hair. Celtic cultures with the pale skin, red toned hair, and pure green eyes. I think these days, it's like playing the lottery.....luck of the draw as to which genes are clicked on or clicked off.

My father's side of the family is of Celtic descent, with some Native American thrown in. My mother's is German descent with a very recent full blooded Cherokee thrown in. Father's side of the family has dark skin, dark hair, and pale, pale blue green eyes. Mother's side is fair skinned, light brown hair, and sky blue eyes. Me....pale skin, red hair, and bright green eyes.

With all the cultural inbreeding and the mix of genetic traits over the millenium, I just feel it's the luck of the draw these days as to what children will look like....no matter the cultural ancestry of the parents.

Eye color can change with age....(and the picture in this link is the color Asmone2 was talking about) Source

And, Source

OK, all. Eye color can change over time because of age or, unfortunately, disease.


Aging, however, is the usual cause of color change over time. Color can change as we age. It does so for 10 to 15% of the normal Caucasian population. These people's eyes change slowly over many years after they reach adolescence.


Investigators considered Caucasians (non-East Asian, non-Native American, non-African) because only Caucasians commonly have lighter eyes.


"Some eyes become darker, but most become lighter with increasing age," says Richard A. Sturm, a Principal Research Fellow at the Institute for Molecular Bioscience at the University of Queensland in Brisbane, Australia.


The basis of human eye color. Pigment cells (yellow in the figure) contain brown pigment granules (shown in various intensities from neutral to light brown to very dark brown). The lighter the pigment and the fewer the granules — the lighter the iris color and the lighter the eye. The circles on the left depict irises and the colors that result from the corresponding pigment cell. Blue irises result from minimal pigment and few pigment granules. Green-hazel irises have moderate pigment levels and number of granules. Brown irises have high pigment levels and many granules. Information from Richard A. Sturm, Institute for Molecular Bioscience at the University of Queensland.

How and why eye color changes.


Pigment in the front layer of the iris (called the stroma) colors the iris. Eye color lightens when pigment granules drop in number, or when the granules make a lighter color. See figure. The iris can also lose color if the pigment degrades. Eyes, unlike skin and hair, do not synthesize color pigment continuously. Instead, eyes keep pigment granules made earlier. So, if the pigment degrades, the eye color lightens.


Likewise, eyes can darken if the number of pigment granules increase or if the granules make darker pigment.


That's how the color changes. Why does it change? Genetics is the key, as experimenters learned by studying twins. They observed the eyes and skin of identical twins and non-identical twins of American Caucasians between the ages of 3 months to 6 years.


Both sets of twins showed a "darkening with age of both the hair and eye colour," says Sturm. The identical twins changed color together, at essentially the same rate. The non-identical twins changed color but at different rates, which indicates a "strong genetic influence in the timing of these colour changes."


Eye color probably changes for the same reason we have one head instead of two: genes. Genes determine all body characteristics — including changing eye color as we age.

reply to post by asmeone2

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After puberty, they won't change from, say, brown to blue. But, they can fade considerably, sometimes to a gray color or to almost no color at all (like a water blue).

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