Within those three billion positions, the regions that determine physical characteristics — skin pigmentation, eye color, hair texture, height, and thousands of other traits — have been increasingly mapped by human genomics research over the past two decades.

Large-scale studies of thousands of living people, comparing their genomes to their observable characteristics, have identified specific genetic variants — specific positions in the genome where the base occupying that position correlates with a particular characteristic.

Skin pigmentation, for example, is determined by the production of melanin — a pigment produced by cells called melanocytes in the skin.

The amount and type of melanin produced is controlled by genes that regulate melanocyte activity.

Dozens of genetic variants across multiple genes contribute to skin color, and modern genomic analysis can examine all of them in a genome to produce a probabilistic assessment of the likely skin pigmentation of an individual.