Cute Redhead - Ballpoint Pen on paper.
The pigment pheomelanin gives red hair its distinctive color. Red hair has far more of the pigment pheomelanin than it has of the dark pigment eumelanin.
The genetics of red hair, discovered in 1997, appear to be associated with the melanocortin-1 receptor (MC1R), which is found on chromosome 16. Red hair is associated with fair skin color because of low concentrations of eumelanin throughout the body of those with red hair. This lower melanin-concentration confers the advantage that a sufficient concentration of important Vitamin D can be produced under low light conditions. However, when UV-radiation is strong (as in regions close to the equator) the lower concentration of melanin leads to several medical disadvantages, such as a higher risk of skin cancer.
The alleles Arg151Cys, Arg160Trp, Asp294His, and Arg142His on MC1R are shown to be recessives for the red hair phenotype. The gene HCL2 (also called RHC or RHA) on chromosome 4 may also be related to red hair.
Red hair is the rarest natural hair color in humans. The non-tanning skin associated with red hair may have been advantageous in far-northern climates where sunlight is scarce. Studies by Bodmer and Cavalli-Sforza (1976) hypothesized that lighter skin pigmentation prevents rickets in colder climates by encouraging higher levels of Vitamin D production and also allows the individual to retain heat better than someone with darker skin. In 2000, Harding et al. concluded that red hair was not the result of positive selection and instead proposed that it occurs because of a lack of negative selection. In Africa, for example, red hair is selected against because high levels of sun would be harmful to untanned skin. However, in Northern Europe this does not happen, so redheads come about through genetic drift.
Estimates on the original occurrence of the currently active gene for red hair vary from 20,000 to 100,000 years ago.
A DNA study has concluded that some Neanderthals also had red hair, although the mutation responsible for this differs from that which causes red hair in modern humans.
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