Blue eyes are due to a gene mutation. Researchers have been looking for her for a long time. And found her somewhere completely different than expected.
Copenhagen – Apparently all blue-eyed people have a match in their family tree. Their common ancestor lived about 6000 and 10000 years ago. This is the result of a study by the University of Copenhagen. He or she inherited a mutation that causes blue eyes.
“Originally, we all had brown eyes,” explains Professor Hans Eiberg from the Department of Cellular and Molecular Medicine in the study. Only with the gene mutation did blue eyes spread all over the world. Exactly how this happened is unclear. The spread may have started when people migrated from Africa to Europe. That would explain why blue eyes are particularly common in Europe.
The mutation for blue eyes is on a different gene than suspected
However, the research team has discovered the biological reason for blue eyes. Scientists had been looking for the gene mutation on the OCA2 gene for years. It determines how much brown pigment is in our eyes. But what the researchers were looking for didn’t even exist.
They found the mutation on a completely different gene called HERC2. HERC2 neutralizes OCA2, the brown pigment, and reveals the blue. It doesn’t turn off the other gene entirely, but limits its action, reducing melanin production in the iris. As a result, the brown color in the eyes is “diluted” to become bluer.
The amount of melanin explains albinism and different eye colors
If the OCA2 gene is not only restricted, but switched off or even destroyed, people have no melanin at all in their hair, eyes or skin color – such a gene mutation leads to what is known as albinism. Those affected are still discriminated against, for example in Africa.
Variations in eye color from brown to green can all be explained by the amount of melanin in the iris. However, blue-eyed people have little 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,” explains Professor Eiberg in the study. “They all inherited the same switch in exactly the same place in their DNA.” In brown-eyed people, on the other hand, there are significant individual differences in the area of DNA that controls melanin production.
A study by the Harvard Medical School has also dealt with a gene mutation: It can apparently protect against Alzheimer’s. (tk)
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