Hair, eye, and skin colour are the most visible phenotypical features of human variability, with a wide range of possibilities that are subject to substantial geographical stratification. In the case of skin pigmentation, people tend to be lighter in colour the further away from the equator, although most of the variation in eye and hair colour is found in the European population. Therefore, the geographical distribution of human skin pigmentation is believed to reflect the history of adaptation to UV radiation levels.
Skin pigmentation is due to the number, type, and distribution of melanosomes, intracellular organelles produced by melanocytes, which contain melanin. This melanin is a black-brown pigment responsible for photoprotection as it absorbs harmful ultraviolet radiation and transforms it into heat. Moreover, its production is stimulated by the incidence of ultraviolet radiation on DNA. Although humans have approximately the same number of melanocytes, there are variations that affect the number, size, and shape of the melanosomes and the amount and type of melanin, which determine an individual's skin colour.
Although a multitude of genes has been identified as being involved in rare diseases associated with skin colour, common variants associated with normal pigmentation have been found in only 6 of them. The most important is SLC24A5, a gene involved in the process of melanin synthesis.
Gene or region studied