Blue Eyes

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Blue Eyes

Postby Beagle » Thu Jan 31, 2008 6:34 pm

http://www.livescience.com/health/080131-blue-eyes.html

People with blue eyes have a single, common ancestor, according to new research.

A team of scientists has tracked down a genetic mutation that leads to blue eyes. The mutation occurred between 6,000 and 10,000 years ago. Before then, there were no blue eyes.

"Originally, we all had brown eyes," said Hans Eiberg from the Department of Cellular and Molecular Medicine at the University of Copenhagen.

The mutation affected the so-called OCA2 gene, which is involved in the production of melanin, the pigment that gives color to our hair, eyes and skin.

"A genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a 'switch,' which literally 'turned off' the ability to produce brown eyes," Eiberg said.

The genetic switch is located in the gene adjacent to OCA2 and rather than completely turning off the gene, the switch limits its action, which reduces the production of melanin in the iris. In effect, the turned-down switch diluted brown eyes to blue.

If the OCA2 gene had been completely shut down, our hair, eyes and skin would be melanin-less, a condition known as albinism.

"It's exactly what I sort of expected to see from what we know about selection around this area," said John Hawks of the University of Wisconsin-Madison, referring to the study results regarding the OCA2 gene. Hawks was not involved in the current study.

Baby blues

Eiberg and his team examined DNA from mitochondria, the cells' energy-making structures, of blue-eyed individuals in countries including Jordan, Denmark and Turkey. This genetic material comes from females, so it can trace maternal lineages.

They specifically looked at sequences of DNA on the OCA2 gene and the genetic mutation associated with turning down melanin production.

Over the course of several generations, segments of ancestral DNA get shuffled so that individuals have varying sequences. Some of these segments, however, that haven't been reshuffled are called haplotypes. If a group of individuals shares long haplotypes, that means the sequence arose relatively recently in our human ancestors. The DNA sequence didn't have enough time to get mixed up.

"What they were able to show is that the people who have blue eyes in Denmark, as far as Jordan, these people all have this same haplotype, they all have exactly the same gene changes that are all linked to this one mutation that makes eyes blue," Hawks said in a telephone interview.

Melanin switch

The mutation is what regulates the OCA2 switch for melanin production. And depending on the amount of melanin in the iris, a person can end up with eye color ranging from brown to green. Brown-eyed individuals have considerable individual variation in the area of their DNA that controls melanin production. But they found that blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes.

"Out of 800 persons we have only found one person which didn't fit — but his eye color was blue with a single brown spot," Eiberg told LiveScience, referring to the finding that blue-eyed individuals all had the same sequence of DNA linked with melanin production.

"From this we can conclude that all blue-eyed individuals are linked to the same ancestor," Eiberg said. "They have all inherited the same switch at exactly the same spot in their DNA." Eiberg and his colleagues detailed their study in the Jan. 3 online edition of the journal Human Genetics.

That genetic switch somehow spread throughout Europe and now other parts of the world.

"The question really is, 'Why did we go from having nobody on Earth with blue eyes 10,000 years ago to having 20 or 40 percent of Europeans having blue eyes now?" Hawks said. "This gene does something good for people. It makes them have more kids."



Archaeologica News. 8)
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Eye colour question

Postby CShark » Thu Jan 31, 2008 8:27 pm

Interesting article B, but I do need clarification on one point: what does this mean for us green-eyed people ? Are green eyes simply less melanin in a brown person's iris, or is there simply a gene for green as I imagine there is a gene for blue. Gotta forgive me if this is not coming out right, my sleeping pill is kicking in, making it fun to type, and even more so, think clearly.

Good post, btw.
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Postby Rokcet Scientist » Thu Jan 31, 2008 9:20 pm

From what I get there is no 'blue gene'. Just a melanin gene that's either more or less turned on. Causing blue irises in the latter case.

All the (many) albinos I've seen, particularly in Africa, had/have electrifying (baby) blue irises.

And aren't green irises really blue irises mottled with brown/gold specks, making it look green?

Then what about grey irises? Where do they fit into this gene scheme?

I have grey/green irises.
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Postby Beagle » Thu Jan 31, 2008 10:16 pm

It's generally accepted that there is a gene for all eye colors. This article makes it seem like a blue-eyed person is just lacking something, but in fact it's a genetic mutation. I'm very surprised at the date, and we'll see if it stands up over time.

I don't know when green eyes first showed up, but they are a distinct color - not a mixture. I, my wife, three children, and one grandson have green eyes. Seems to predominate in people of Scottish descent.
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Postby zale » Fri Feb 01, 2008 3:45 am

Is there ANY possibility that blue eyes were introduced by the neanderthals?
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Postby gunny » Fri Feb 01, 2008 5:57 am

Melanin needed in Africa climes, not in the north. Skin and eyes became less brown or black. Yes, very possible Neanderthals, many mils in nothern Europe, had blue eyes, blond hair, white skin. We need to find one in a glacier ice crevace.
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Postby Digit » Fri Feb 01, 2008 8:04 am

Blue eyed people are more prone to cataracts, so would be at a disadvantage in hot climes or under clear skies.
Logic therefore says it would probably have originated in the higher latitudes, this would make HSN a candidate.
First people deny a thing, then they belittle it, then they say it was known all along! Von Humboldt
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Cataracts and eye colour

Postby CShark » Fri Feb 01, 2008 3:05 pm

Digit wrote:Blue eyed people are more prone to cataracts, so would be at a disadvantage in hot climes or under clear skies.
Logic therefore says it would probably have originated in the higher latitudes, this would make HSN a candidate.


Actually, that is not correct. Brown-eyed people are more prone to cataracts : (took a while to find this ref!): http://www.sciencedirect.com/science?_o ... 2ecbe84916

Sorry about the long link.

BTW, there are genes for eye colour, just there are genes for hair colour and pattern baldness.
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Postby Digit » Fri Feb 01, 2008 3:11 pm

Can't argue with that Shark. But as blued eyed cataract sufferer it ain't what my optician told me!
First people deny a thing, then they belittle it, then they say it was known all along! Von Humboldt
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Cataracts

Postby CShark » Fri Feb 01, 2008 3:17 pm

Digit wrote:Can't argue with that Shark. But as blued eyed cataract sufferer it ain't what my optician told me!


Bummer Dig, sorry to hear about that.
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Postby Digit » Fri Feb 01, 2008 3:20 pm

They're not bad Shark, you learn to live with these things as you age.
First people deny a thing, then they belittle it, then they say it was known all along! Von Humboldt
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I hear ya

Postby CShark » Fri Feb 01, 2008 7:55 pm

Digit wrote:They're not bad Shark, you learn to live with these things as you age.


Yes, sadly I know all about that. :( Turned the big 5-0 this past fall; a month later was diagnosed with fibromyalgia. Till last spring was playing 4 hockey games a week and was at the gym pretty much every day. Now, I'm on so many #@@$! meds I need baggies to keep them organized!

On a happier note, now I have more time to pursue a few of my other passions, including the study of british history.

Cheers
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Postby Digit » Sat Feb 02, 2008 3:28 am

Sound like a bad year all round Shark. My wife was diagnosed with type 'B' Diabetes, I was diagnosed with Prostate cancer and now you!
My mother's New Year toast was always may the New Year be as good as the old!'
First people deny a thing, then they belittle it, then they say it was known all along! Von Humboldt
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Postby War Arrow » Sat Feb 02, 2008 6:28 am

Sorry - bit off topic, but whilst I haven't had so tough a time as yourself, Dig - this new year's eve has been the first one I can remember swapping my usual 'hmph - I'm not celebrating, I kind of enjoyed the year just gone' for 'well thank f*** THAT's over and done with.' Everyone seems to have had a crap 2007.

Sorry, on with the blue eyes. Which I have by the way, so thanks for the warning re - cataracts.
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Tough 07

Postby CShark » Sat Feb 02, 2008 9:31 am

Digit wrote:Sound like a bad year all round Shark. My wife was diagnosed with type 'B' Diabetes, I was diagnosed with Prostate cancer and now you!
My mother's New Year toast was always may the New Year be as good as the old!'


Prostate cancer....not good. Did they catch it early ? As I think I mentioned, I underwent a recent surgery, in which they did remove some of the prostate. My biopsy turned out negative, thank God.
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