....SLC24A5 appears to have played a key role in the evolution of light skin in humans of European ancestry. The gene's function in pigmentation was discovered in zebrafish as a result of the positional cloning of the gene responsible for the "golden" variety of this common pet store fish.
In this work, cancer geneticist Keith Cheng used electron microscopy to characterize the cellular mechanism underlying the lighter color of golden zebrafish, and noted a striking similarity between the changes of melanocytes (pigment cells) in those lighter-skinned fish and lighter-skinned humans (in particular, Europeans). This led Cheng to ask his Pennsylvania State University colleague, anthropologist Mark D. Shriver, whether he had human DNA linked to skin color measurements. Shriver, who collaborates internationally to study the basis of variation in human skin color and other features in human populations, pointed to the then-new International HapMap Project database of genetic variation in human populations, and found that the gene has a single "coding" polymorphism - one that changes an amino acid. The two primary alleles differ in only one nucleotide, changing the 111th amino acid from alanine to threonine, abbreviated "A111T".
The threonine allele was present in 98.7 to 100% among several European samples, while the alanine form was found in 93 to 100% of samples of Africans, East Asians and Indigenous Americans. The variation is a SNP polymorphism rs1426654, which had been previously shown to be second among 3011 tabulated SNPs ranked as ancestry-informative markers. Collaborator Victor Canfield plotted the human data to estimate that this single change in SLC24A5 explains between 25 and 38% of the difference in skin melanin index between peoples of West African vs. European Ancestry.
The discovery of this gene has interesting social implications because the "derived" European allele was derived by mutation from the ancestral gene sequence. As noted by Penn State's Victor Canfield, the ancestral alanine is conserved in all vertebrates sequenced to date, mutant only in the European allele, but only rarely in West African or East Asian (primarily Chinese, Japanese and Korean) populations (presumably by admixture). Furthermore, the European mutation is associated with the largest region of diminished genetic variation in the CEU HapMap population, suggesting the possibility that the A111T mutation may be the subject of the single largest degree of selection in human populations of European ancestry. Selection for the derived allele is based on the need for sunlight to produce the essential nutrient, vitamin D. In northerly latitudes, there is less sun, greater requirement for body coverage due to colder climate, and frequently, diets poor in vitamin D, making lighter skin necessary for survival. Tests for this variation has obvious application to forensic science.
........There is no such thing as race........