Skin pigmentation

Skin color is a highly variable trait with a wide spectrum of possibilities from almost black to almost white. It is determined by the amount and type of melanin and is closely related to eye and hair color. This color variation is mostly due to genetics.

Skin color is a highly variable trait, linked to genetics and geographic distribution. It is the result of the amount and type of melanin, a natural pigment that is also responsible for hair color and whose function is to absorb harmful UV radiation. Melanins are found in all individuals, forming complex combinations that give rise to the many shades of skin color. In general, there are two types of melanins, eumelanin, which is dark in color, and pheomelanin, which is light in color. In general, it is the amount of eumelanin that will determine skin color, although pheomelanin is especially present in redheads.

Melanins are produced by melanocytes, located in the basal layer of the dermis and in the hair follicle. Different human ethnicities have approximately the same number of melanocytes, but dark-skinned people have a higher cellular activity.

Dark skin is richer in pigments that provide superior protection against the harmful effects of ultraviolet radiation. It is associated with tropical regions and high UV radiation.

Light skin is associated with low UV radiation environments such as subtropical regions. This skin type has better UV absorption qualities and is more efficient in vitamin D synthesis.

Brown skin is the intermediate color type between light and dark skin. In this type, melanosomes provide moderate protection against the harmful effects of UV radiation. It is mainly associated with tropical regions such as India, Polynesia and the Middle East, although it is widely distributed throughout the world. Both fair and brown skin can change its tone as a result of exposure to the sun, although the latter tans more easily.

Skin pigmentation and color is a highly heritable trait, highly associated with geographic ancestry. One of the largest GWAS studies to date, involving almost 360000 participants, identified 193 markers associated with the expression of this trait, including the OCA2 gene, a melanocyte transporter protein common to other traits such as albinism, and the TYR gene, a gene that is associated with the expression of the OCA2 gene.The TYR gene, which is responsible for the production of the enzyme tyrosine in melanocytes, and the OCA2 gene, a melanocyte transporter protein common to other traits such as albinism, were identified.

Number of observed variants

13.5 million variants

Number of loci analyzed in the study

193 loci

Bibliography

UK Biobank Database. Skin colour, Data-Field 1717 [Version Feb-2022]

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