I found this interesting in a genealogy sort of way. This article is reproduced from World Science and is courtesy of the University of Copenhagen.
New research has found that blue-eyed people have one, common ancestor who lived between 6,000 and 10,000 years ago. At some point then-a time by which humans were in most of Earth’s livable areas, agriculture was spreading and the first civilizations were forming-a mutation produced blue eyes, University of Copenhagen biologists say.
“Originally, we all had brown eyes,” said one of the researchers, Hans Eiberg. But a mutation affecting a gene called OCA2 “resulted in the creation of a ‘switch’ which literally turned off the ability to produce brown eyes.”
The gene, he explained, codes for the production of a protein involved in producing melanin, the pigment that gives colour to our hair, eyes and skin.
The “switch” is located not within the gene, but in a directly neighboring gene; yet it influences OCA2, Eiberg said. The result is a reduction in the production of melanin in the iris-effectively “diluting” brown eyes to blue, Eiberg went on. If it turned off melanin production completely, he said, it would produce albinos, or people without pigment in their hair, skin or eyes.
The findings appear in the Jan. 3 online issue of the research journal Human Genetics.
Eye colour variation from brown to green is all caused by the amount of melanin in the iris of the eye, Eiberg explained, but the blue-eyed have only slight variation in this amount. “From this we can conclude that all blue-eyed individuals are linked to the same ancestor… they have all inherited the same switch at exactly the same spot in their DNA.” Unlike them, brown-eyed people vary considerably in the area of their DNA that controls melanin production, he added.
Eiberg and colleagues examined DNA from the mitochondria, a cellular compartment passed down only through mothers. They also compared eye colour of blue-eyed people from in countries as diverse as Jordan, Denmark and Turkey. The findings are the latest in a decade of genetic research that Eiberg said began in 1996, when he first implicated the OCA2 gene in eye colour.
The mutation of brown eyes to blue is neither positive nor negative, Eiberg said; rather, it’s one of several mutations such as hair colour, baldness, freckles and beauty spots, which neither raise nor reduce a person’s survival chances. “It simply shows that nature is constantly shuffling the human genome,” he said, “creating a genetic cocktail of human chromosomes and trying out different changes.”
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