Probability of having red hair

Red hair color is the result of the combination of two types of melanin pigments in specific amounts, which ultimately determines the characteristic orange color. In addition, this characteristic production of melanin pigments can also determine the color of the skin or even the eyes together.

Red hair coloration is due to the production of pheomelanin and very little eumelanin. Pheomelanin consists of a photosensitive pigment that gives it a red or light maroon-pink color, giving rise to the characteristic orange hair color. Eumelanin, on the other hand, is a dark brown or black pigment, so its low concentration results in light blond hair, and thus the red hair color is hidden when a higher amount of eumelanin is present. Additionally, the color of the hair can vary throughout life, especially with age as melanin production decreases over time, and is conditioned by environmental factors such as sun exposure.
The presence of red hair occurs in Caucasian populations and is generally associated with lighter skin pigmentation and the presence of freckles, although this is not necessarily always the case. It is also usually related to green, hazel and amber eye color, due to the presence of pheomelanin. The highest frequency of redheads is found in northwestern Europe, for example, in Scotland, 13% percent of the population has red hair followed in frequency by Ireland. In the Rif region of Morocco and Kazan (Russia) it is also characteristic due to European migrations and the isolation of these population groups, although nowadays, also due to migrations, redheads can be found all over the European continent, the United States, Australia etc.

Hair color is a highly heritable trait with a complex genetic architecture. It is a trait whose frequency is greatly affected by the geographical origin of the individual. Four markers associated with the probability of having red hair color have been identified from studies involving people of European ancestry, including genome-wide association studies (GWAS). These markers are found in the MC1R gene, a gene that produces the melanocortin 1 receptor, a protein involved in the development of skin color and hair color in mammals from melanin synthesis by melanocytes. It is estimated that approximately 70% of people with two variants in the MCR1 gene have red hair.

Number of observed variants

13.5 million variants

Number of variants analyzed in the study

4 variants

Bibliography

Liu F et al. Colorful DNA polymorphisms in humans. Semin Cell Dev Biol. 2013;24(6-7):562-75.

Ito S et al. Diversity of human hair pigmentation as studied by chemical analysis of eumelanin and pheomelanin. J Eur Acad Dermatol Venereol. 2011;25(12):1369-80.

Eriksson N et al. Web-based, participant-driven studies yield novel genetic associations for common traits. PLoS Genet. 2010;6(6):1–20.

Han J et al. A genome-wide association study identifies novel alleles associated with hair color and skin pigmentation. PLoS Genet. 2008;4(5).

Sulem P et al. Two newly identified genetic determinants of pigmentation in Europeans. Nat Genet. 2008;40(7):835–7.p>

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