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    Blue-Eyed People Have One Common Ancestor
    By News Staff | January 30th 2008 08:19 PM | 9 comments | Print | E-mail | Track Comments
    A team at the University of Copenhagen have tracked down a genetic mutation which took place 6-10,000 years ago and is the cause of the eye color of all blue-eyed humans alive on the planet today.

    What is the genetic mutation?

    “Originally, we all had brown eyes”, said Professor Eiberg from the Department of Cellular and Molecular Medicine. “But 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.”

    The OCA2 gene codes for the so-called P protein, which is involved in the production of melanin, the pigment that gives color to our hair, eyes and skin. The “switch”, which is located in the gene adjacent to OCA2 does not, however, turn off the gene entirely, but rather limits its action to reducing the production of melanin in the iris – effectively “diluting” brown eyes to blue. Therefore the switch’s effect on OCA2 is very specific.

    If the OCA2 gene had been completely destroyed or turned off, human beings would be without melanin in their hair, eyes or skin color – a condition known as albinism.

    Different eye color phenotypes. a Blue (without brown areas). b Blue with brown spots (with brown) scored as “unknown” in the linkage and association studies. c Brown–green/hazel (BEY1) with a board puripupillary ring. d Brown (BEY2), total brown pigmentation. The person with blue eye color (a) represents the genotype rs12913832 G/G, while the persons b–d represent the genotype rs12913832 A/G



    Limited genetic variation

    Variation in the color of the eyes from brown to green can all be explained by the amount of melanin in the iris, but blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes.

    “From this we can conclude that all blue-eyed individuals are linked to the same ancestor,” says Professor Eiberg. “They have all inherited the same switch at exactly the same spot in their DNA.”

    Brown-eyed individuals, by contrast, have considerable individual variation in the area of their DNA that controls melanin production.

    Professor Eiberg and his team examined mitochondrial DNA and compared the eye color of blue-eyed individuals in countries as diverse as Jordan, Denmark and Turkey. His findings are the latest in a decade of genetic research, which began in 1996, when Professor Eiberg first implicated the OCA2 gene as being responsible for eye color.

    Nature shuffles our genes

    The mutation of brown eyes to blue represents neither a positive nor a negative mutation. It is one of several mutations such as hair color, baldness, freckles and beauty spots, which neither increases nor reduces a human’s chance of survival. As Professor Eiberg says, “It simply shows that nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so.”

    Article: Hans Eiberg, Jesper Troelsen, Mette Nielsen, Annemette Mikkelsen, Jonas Mengel-From, Klaus W. Kjaer, Lars Hansen, Blue eye color in humans may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression, Human Genetics, 10.1007/s00439-007-0460-x.

    Comments

    vergon
    Wake me up when we mutate to glow-in-the-dark eyes.
    Vergon
    stevelong100
    Follow-up story: BOTH BLUE-EYED AND BROWN-EYED PEOPLE BOTH DESCENDED FROM GELATINOUS PRE-CAMBRIAN ROD-LIKE CREATURE THAT HAD NO MOUTH OR ANUS Some ancestor seekers may be disappointed in dear old Great... Granddad. He didn't even have one eye, much less two blue ones. He lived in the muck and was about one cm long. But nevertheless he is Father of us all (or perhaps father and mother, since he didn't need anyone else to start the family that is us.) One observer was heard to comment, "He looks just like my cousin George." Most however were glad to know that they were ultimately descended from a single individual, rather than a whole bunch of different individuals. "It makes me feel special," said one of the few people in the room with one blue eye and one brown one. No three eyed people were present at the time of the press conference...
    So why wasn't this recessive trait swamped in the existing brown-eyed population shortly after it appeared?

    Even if people were lining up to marry the lucky blues, it's hard to believe there were enough of them to keep it going.

    This is a frequent mistake. Just because a trait is recessive or uncommon does not imply it is headed for extinction. That is not the way genetics works.

    I disagree that blue irises are not a positive mutation -- not for survival value but instead for sexual attractiveness.

    This certainly worked in my genome's advantage during my time in Japan :)

    I was under the impression that the blue eye mutation would be useful in areas with low light due to atmospheric moisture. Is there any evidence to prove that blue eyes help see in foggy/misty weather?
    Not sure where I read this, Jared Diamond maybe?
    From the web:
    People with blue eyes retain their 20/20 vision for less time in life than people with brown or green eyes. People with blue eyes have less reflective material in their iris so that sunlight is absorbed more against the optic nerve.
    https://cornellbiochem.wikispaces.com/Jamie%27s+Mutation+Project

    LauraHult

    with my grey eyes, I feel pretty left out. What about green eyes?

    We are entirely made up of mutations! I don't understand why this is news and I'm tired of stumbling it!