Web address:
http://www.sciencedaily.com/releases/2008/01/
080130170343.htm
Blue-Eyed Humans Have A Single, Common Ancestor
enlarge
Variation in the colour 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. (Credit:
iStockphoto/Cristian Ardelean)
Jan. 31, 2008 New research shows that people with blue eyes have a single,
common ancestor. 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 colour 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 colour 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. The switch's effect on
OCA2 is very specific therefore. If the OCA2 gene had been completely destroyed
or turned off, human beings would be without melanin in their hair, eyes or
skin colour a condition known as albinism.
Limited genetic variation
Variation in the colour 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
colour 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 colour.
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 colour, 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."
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Story Source:
The above story is reprinted from materials provided by University of
Copenhagen.
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University of Copenhagen (2008, January 31). Blue-eyed Humans Have A Single,
Common Ancestor. ScienceDaily. Retrieved March 2, 2013, from
http://www.sciencedaily.com /releases/2008/01/080130170343.htm
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