What this means

SLC24A5 codes for a calcium/potassium exchanger in the melanosome — the organelle where melanin is made. A single amino-acid change (A111T, the rs1426654 variant) reduces melanin output and accounts for a striking fraction (somewhere between a third and a half) of the skin pigment difference between European and West African populations. It is one of the strongest examples of a single coding change with a large visible effect, and a textbook case of recent positive selection in human populations migrating to higher latitudes.

SLC24A5 is a gene that moves ions in and out of the tiny compartments where your skin makes pigment. A single DNA change reduces how much pigment gets made — and that one change accounts for somewhere between a third and half of the skin colour difference between Europeans and West Africans. It's one of the clearest examples of a single tweak with a big visible effect, and one of the strongest signs that humans evolved lighter skin quickly after moving to higher latitudes.

Caveats

• Skin pigmentation is polygenic — SLC24A5 is one of many contributing genes.
• Tanning, vitamin D status, and sun exposure all shape phenotype on top of genotype.
• The "light" allele is near-universal in European populations, so it carries little within-Europe predictive value.
• This variant is most informative in populations with mixed ancestry.

References

• Lamason et al. — SLC24A5, a putative cation exchanger, affects pigmentation in zebrafish and humans (Science, 2005)
• Norton et al. — Genetic evidence for the convergent evolution of light skin in Europeans and East Asians (Molecular Biology and Evolution, 2007)