BLUE EYES In 2008, new research suggested that people with blue eyes have a single common ancestor. Scientists tracked down a genetic mutation that leads to blue eyes. Originally, we all had brown eyes, said Eiberg.[30] Eiberg and colleagues showed in a study published in Human Genetics that a mutation in the 86th intron of the HERC2 gene, which is hypothesized to interact with the OCA2 gene promoter, reduced expression of OCA2 with subsequent reduction in melanin production.[31] The authors concluded that the mutation may have arisen in a single individual probably living in the northwestern part of the Black Sea region 6,000–10,000 years ago during the Neolithic revolution.[30][31][32] Eiberg stated, 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. He added: The genetic switch is located in the gene adjacent to OCA2 and rather than completely turning off the gene, the switch limits its action, which reduces the production of melanin in the iris. In effect, the turned-down switch diluted brown eyes to blue. If the OCA2 gene had been completely shut down, our hair, eyes and skin would be melanin-less, a condition known as albinism.[30] In Estonia, 99% of people have blue eyes, stated Hans Eiberg from the Department of Cellular and Molecular Medicine at the University of Copenhagen.[33] Blue eyes are also common in other parts of northern and eastern Europe, particularly around the Baltic Sea. Eiberg added, In Denmark 30 years ago, only 8% of the population had brown eyes, though through immigration; today that number is about 11%. In Germany, about 75% have blue eyes.[33] Blue eyes are also found in southern Europe, Central Asia, South Asia, and West Asia, especially among the Jewish population of Israel.[34][35][36] Many modern Israeli Jews are of European Ashkenazi origin, among whom this trait is common (A study taken in 1911 found that 53.7% of Ukrainian Jews had blue eyes).[37][38] DNA studies on ancient remains suggest that blue eyes were present in a wide geographical range by the Bronze Age, though there are too few skeletons to estimate frequencies. A hunter-gatherer dating to approximately 5,000 BCE at the La Braña-Arintero site in León, Spain, had blue eyes, brown skin tone, and Y-DNA haplogroup C6.[39] DNA testing performed on ancient Scythian skeletons found that light eye colors were already present during the Bronze and Iron Ages in the Siberian Krasnoyarsk region.[40] 10 out of the 11 subjects carried Y-DNA R1a1, most commonly found today in Eastern Europe and South Asia.[41][42][43] A 2002 study found that the prevalence of blue eye color among the white population in the United States to be 33.8% for those born from 1936 through 1951 compared with 57.4 percent for those born from 1899 through 1905.[13] As of 2006, one out of every six people, or 16.6% of the total population, and 22.3% of whites, has blue eyes. Blue eyes are continuing to become less common among American children.[44]
Posted on: Sat, 09 Aug 2014 20:43:44 +0000