Reeling in the gene that makes Caucasians white
[Originally from The Times, reprinted in The Australian newspaper Dec 17, 2005]
LONDON: A newly identified gene that humans share with fish has been found to help explain why white people have pale skins.
Scientists in the US have discovered that a tiny mutation in a gene plays a key role in determinating skin colour, with Caucasians inheriting a different version from other racial groups.
While it is known that colour is genetically determined, this is the first research to pinpoint a particularly stretch of DNA that underlies normal differences in human pigmentation.
The findings promise new insights into cancer and other diseases influneced by genes and shed light on the eevolution of different hues of skin. The discovery of the gene, named slc245a5, has emerged from research into cancer that used zebrafish as an animal model.
A team led by Keith Cheng, of Pennsylvania State University, noted that a varieant of the fish, known as "golden", had paler markings than usual, and that this lighter pigmentation was caused by a mutation in slc245a5. As the gene is known to exist in people, Dr Cheng wonderred whether it might be reponsible for some of the variation in human skin colour.
First he transplanted the human gene into fish and found that it had the same effect on pigmentation. He then teamed up with a colleague, Mark Shriver, to investigate ho different versions of the gene were distrubted across human populations, using the recently completed HapMap, which charts genetic variation.
The researchers have found that while people of African and Chinese origin carry on version of slc245a5, those of white European ancestry have a different one. The results, published in the journal Science, strongly indicate a big influence over skin colour.
The work suggests that the dark version of the gene occurs as a default, and that the light variant is a mutation that probably evolved as humans moved out of Africa and migrated into northern latitudes. This supports a theory that lighter skin evolved as an adaptation to the weaker sunlight of northern climes.
Sunlight is essential for the body to manufacture vitamin D, and pale skins make this easier when the sun's rays are not particulary strong. The slc245a5 gene does not vary between Africans and much lighter-skinned Chinese, or between Europaeans of Swedish and Greek ancestry.
It is thought to be responsible for between 25 and 38 per cent of colour variation between Europeans and Africans, and other genes are certain to be involved.
While genes that are mutated in albino people have been identified, this is the first that has a major influence on normal variations. The results may assist research into malignant melanona, the deadliest skin cancer, which is rarer among dark-skinned people.
They should also help scientists seeking to tease out the genetic contribution to conditions such as heart disease and diabetes, which are often influenced by multiple genes.