Blue eyes result of ancient genetic ‘mutation’
By Roger Highfield, Science Editor
Last Updated: 7:01am GMT 30/01/2008
Frank Sinatra, Stephen Hawking, Marie Curie and Stephen Fry all owe their blue eyes to a genetic
mutation that likely occurred between 6,000 and 10,000 years ago, researchers say.
Scientists believe they have tracked down the cause of the eye colour of all blue-eyed humans on
the planet today.
"Originally, we all had brown eyes", said Prof Hans Eiberg from the University of
Copenhagen, who led the team.
Blue eye colour most likely originated from the near east area or northwest part of the Black Sea
region, where the great agriculture migration to the northern part of Europe took place in the
Neolithic periods about six–10,000 years ago.
"That is my best guess," he said. "It could be the northern part of
Afghanistan."
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The mutation affected a gene called OCA2 and "literally ‘turned off’ the ability to produce
brown eyes", he says.
OCA2 is involved in the production of melanin, the pigment that gives colour to hair, eyes and
skin.
The mutation in the adjacent gene does not switch off the OCA gene entirely but limits its
action, reducing the production of melanin in the iris of the eye – "diluting" brown
eyes to blue.
If the OCA2 gene had been completely turned off, those who inherited this mutation would be
without melanin in their hair, eyes or skin colour – albino.
For the study, Prof Eiberg’s team examined DNA in blue-eyed individuals in countries as diverse
as Jordan, India, Denmark and Turkey.
His findings are the latest in a decade of genetic research, which began in 1996, when Prof
Eiberg first implicated the OCA2 gene as being one of those responsible for eye colour.
"They have all inherited the same switch at exactly the same spot in their DNA. From this we
can conclude that all blue-eyed individuals are linked to the same ancestor," said Prof Eiberg,
who reports the work in the journal Human Genetics.
http://www.foxnews.com/story/0,2933,327070,00.html
Scientist: All Blue-Eyed People Are Related
Friday, February 01, 2008
If you’ve got blue eyes, shake the hand of the nearest person who shares your azure irises: He or
she may be a distant cousin.
Danish researchers have concluded that all blue-eyed people share a common ancestor, presumably
someone who lived 6,000 to 10,000 years ago.
"Originally, we all had brown eyes," Professor Hans Eiberg of the of Copenhagen said in
a press release. "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."
That "switch" — a simple change from "A," or adenine, to "G," or
guanine, in the DNA — actually sits next to the OCA2 gene, which regulates the pigmentation of our
eyes, hair and skin, and hence has only a limiting effect on it.
If the mutation had completely deactivated OCA2, all blue-eyed people would be albinos.
Eiberg and his team analyzed 155 individuals in a large Danish family, plus several blue-eyed
people born in Turkey and Jordan.
All blue-eyed subjects had the mutation, and there was very little variation on the genes
neighboring it on the chromosome, indicating that the mutation first arose relatively recently.
In contrast, most mammals share the "normal" form of the gene. The six-letter sequence
is exactly the same among mice, horses, cows, rats, dogs, cats, monkeys, chimpanzees and humans with
brown eyes. (No word on what gives Siberian huskies and Siamese cats blue eyes.)
Eiberg figures the mutation took place on the northern of the Black Sea, but that’s an educated
guess, assuming the first blue-eyed humans were among the proto-Indo-Europeans who subsequently
spread agriculture into western Europe and later rode horses into Iran and India.
Ironically, neither the first person to have the mutation, nor his or her children, would have
had blue eyes themselves.
Blue eyes are a recessive trait, and the gene must be inherited from both parents. (Green eyes
involve a related but different gene, one that is recessive to brown but dominant to blue.)
It wasn’t until the original mutant’s grandchildren or great-grandchildren hooked up — cousin
marriage is the norm through most of human history — that the first blue-eyed person appeared. He
or she must have looked pretty odd for the Neolithic era.
Eiberg stresses that the genetic variation, as the press release puts it, is "neither a
positive nor a negative mutation."
That’s a bit disingenuous, as the mutation also produces greater instance of blond hair (sexually
selected for even today) and fair skin, which confers a survival advantage by stimulating greater
production of vitamin D in sun-starved northern European countries — exactly where blue eyes are
still most prevalent.
Journal article: http://www.springerlink.com/content/2045q6234h66p744/fulltext.html