WASHINGTON, Oct 22 (Reuters) A few dozen genetic changes can help explain why people of European descent have so many different shades of hair, eye and skin color -- but it is still impossible to tell the color of someone's eyes or hair based on DNA alone, researchers said yesterday.
The team at Decode Genetics said their scans of 7,000 Icelandic and Dutch people found 60 separate genetic mutations linked with hair, eye and skin color.
As with earlier gene surveys, no single mutation or cluster of mutations can tell whether a person has brown, blue or green eyes; brown, blond or red hair or whether his or her skin is fair or freckled.
But, writing in the journal Nature Genetics, Kari Stefansson of Decode Genetics and colleagues said their new suite of genes help narrow down the possibilities and might be used to study certain diseases that are more common in people with certain coloring.
''It has long been thought that before the migrations that first brought our species out of Africa some 60,000 years ago, ancestral human populations had characteristically dark skin, eyes and hair,'' the researchers wrote.
In Europe, humans evolved big variations in skin, eye and hair color. But skin and hair tends to be darker in populations originating from near the equator, which supports the idea that pigmentation helps protect from the sun's radiation.
It is unclear why people living in the North -- including not only Europeans but many Asians -- have lighter skin.
''The most obvious functional advantage of lighter skin pigmentation in northerly latitudes is that it facilitates the synthesis of vitamin D3 in spite of low levels of ultraviolet radiation exposure,'' the researchers wrote.
MYSTERIOUS VARIATIONS And the big variations in eye and hair color among Europeans are even more mysterious.
Stefansson's team found evidence that these variations are heavily selected for, however -- meaning people who have them were more likely to reproduce and pass them along to offspring. This could be because they provide a survival advantage, or merely because people liked such traits and tended to choose mates who have them.
The researchers found 60 different single nucleotide polymorphisms, or SNPs, associated with red, blond or brown hair, brown, blue or green eyes, freckles and skin sensitivity to sunlight.
SNPs are single-letter changes in the genetic code.
''The 60 SNPs were clustered in different genomic regions along five different chromosomes (6, 12, 14, 15 and 16),'' they said.
Most just predicted a tendency to have, for instance, green versus blue eyes or brown versus blue eyes.
''A SNP on chromosome 6p25 is associated with an increased likelihood of freckles and skin sensitivity to sunlight, as well as to brown hair,'' they added.
Decode, which aims to develop tests to market for various diseases and other uses, said the findings may help ''forensic geneticists and for studies of diseases of the skin and eyes that are known to be correlated with such traits.'' REUTERS SS AS0834