Blue eyes

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Palmela

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Blue eyes have their hue because of a single genetic mutation that occurred fewer than 10,000 years ago in one individual and swept rapidly through the European population, according to a study published in the journal Human Genetics in January.

After studying some 800 individuals from Denmark, Turkey, and Jordan, the researchers pinpointed a single base-pair change in the human genome that showed up in all the blue-eyed people and none of the brown-eyed people. “There was one founder mutation that gave rise to all the people in Europe who have blue eyes,” says report coauthor Jesper Troelsen, a University of Copenhagen molecular biologist. “It was quite surprising.”Those with blue eyes also shared a number of other genetic markers in the same region—a stretch of DNA that regulates production of the pigment melanin. The tweak causes the iris to manufacture less melanin, lending the eyes their lighter shade.

As DNA passes down through generations, it gets shuffled and reshuffled. Because this particular stretch of DNA was so similar—barely shuffled—among all the blue-eyed people studied, the researchers inferred that the blue-eyes mutation is fairly young. Its apparently rapid spread through the population also suggests that, evolutionarily speaking, the mutation had something to offer. “It’s difficult to know what happened 10,000 years ago,” Troelsen says, but blue eyes may be linked with other traits—such as light skin color—that came in handy for early northern Europeans.
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http://discovermagazine.com/2009/jan/042




One Common Ancestor Behind Blue Eyes
31 January 2008

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



In conclusion, we have identified a conserved regulatory element within intron 86 of the HERC2 gene that is perfectly associated with the brown/blue eye color in studied individuals from Denmark, Turkey and Jordan. This element had an inhibitory effect on the OCA2 promoter activity in cell cultures, and the blue and the brown alleles were shown to bind non-identical subsets of nuclear extracts. In total, all these data strongly support a model where the blue eye color in humans is caused by homozygosity of the rs12913832*G allele.
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http://www.springerlink.com/content/2045q6234h66p744/fulltext.html
 
Blue eyed ancestor must have been a babe magnet of note! Thanks great great great x1000 grandad!
 
i have blue cataracts but sometimes my daughter says they are green so ek weet nie.
 
I once read that people with brown eyes have, theoretically, faster reaction times than blue-eyed people.

BTW I've got blue eyes. :(
 
Blue eyes in lemurs and humans: same phenotype, different genetic mechanism.

Bradley BJ, Pedersen A, Mundy NI.

Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK. [email protected]

Almost all mammals have brown or darkly-pigmented eyes (irises), but among primates, there are some prominent blue-eyed exceptions. The blue eyes of some humans and lemurs are a striking example of convergent evolution of a rare phenotype on distant branches of the primate tree. Recent work on humans indicates that blue eye color is associated with, and likely caused by, a single nucleotide polymorphism (rs12913832) in an intron of the gene HERC2, which likely regulates expression of the neighboring pigmentation gene OCA2. This raises the immediate question of whether blue eyes in lemurs might have a similar genetic basis. We addressed this by sequencing the homologous genetic region in the blue-eyed black lemur (Eulemur macaco flavifrons; N = 4) and the closely-related black lemur (Eulemur macaco macaco; N = 4), which has brown eyes. We then compared a 166-bp segment corresponding to and flanking the human eye-color-associated region in these lemurs, as well as other primates (human, chimpanzee, orangutan, macaque, ring-tailed lemur, mouse lemur). Aligned sequences indicated that this region is strongly conserved in both Eulemur macaco subspecies as well as the other primates (except blue-eyed humans). Therefore, it is unlikely that this regulatory segment plays a major role in eye color differences among lemurs as it does in humans. Although convergent phenotypes can sometimes come about via the same or similar genetic changes occurring independently, this does not seem to be the case here, as we have shown that the genetic basis of blue eyes in lemurs differs from that of humans. Copyright 2009 Wiley-Liss, Inc.

Publication Types:
Research Support, Non-U.S. Gov't

PMID: 19278018 [PubMed - in process]

http://www.ncbi.nlm.nih.gov/pubmed/19278018?dopt=Abstract
 
Blue eyes! Baby's got blue eyes!

/humming Elton John's tune :)

My boy's got clear blue eyes and my missus she's got slightly more green. She's professional nurse and is always telling me about genetics. Fascinating!
 
Blue eyes are more prone to light sensitivity, I have severe light sensitivity and have to wear shades, bright light influences my mood too - makes me irritated followed by a slightly bad mood.
 
wrathex, try not wearing shades for 4 months

or, can you remember having that problem growing up?

If I wear shades for 4 days while say - on the beach on holiday, my eyes become sensitive to light, and I have to keep wearing the shades. But, if I stop wearing the shades completely, my eyes are fine. The transition requires a period of non-sunny weather, for like 2 days or so without wearing shades. But, then when the sun arrives ... cool bananas.
 
I didn't read it all but this was obviously one horny bastard!

a single genetic mutation that occurred fewer than 10,000 years ago in one individual and swept rapidly through the European population
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