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 low concentrations of eumelanin throughout the body of those with red hair caused by a MC1R mutation can cause both. The lower melanin concentration in skin 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 MC1R recessive variant gene that gives people red hair and non-tanning skin is also associated with freckles, though it is not uncommon to see a redhead without freckles Eighty percent of redheads have an MC1R gene variant, and the prevalence of these alleles is highest in Scotland and Ireland.
Red hair can originate from several changes on the MC1R-gene. If one of these changes is present on both chromosomes then the respective individual is likely to have red hair. This type of inheritance is described as an autosomal recessive mode of inheritance. Even if both parents do not have red hair themselves, both can be carriers for the gene and have a redheaded child.
Genetic studies of dizygotic (fraternal) twins indicate that the MC1R gene is not solely responsible for the red hair phenotype; unidentified modifier genes exist, making variance in the MC1R gene necessary, but not always sufficient, for red hair production.
Origins
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.
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 low concentrations of eumelanin throughout the body of those with red hair caused by a MC1R mutation can cause both. The lower melanin concentration in skin 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 MC1R recessive variant gene that gives people red hair and non-tanning skin is also associated with freckles, though it is not uncommon to see a redhead without freckles Eighty percent of redheads have an MC1R gene variant, and the prevalence of these alleles is highest in Scotland and Ireland.
Red hair can originate from several changes on the MC1R-gene. If one of these changes is present on both chromosomes then the respective individual is likely to have red hair. This type of inheritance is described as an autosomal recessive mode of inheritance. Even if both parents do not have red hair themselves, both can be carriers for the gene and have a redheaded child.
Genetic studies of dizygotic (fraternal) twins indicate that the MC1R gene is not solely responsible for the red hair phenotype; unidentified modifier genes exist, making variance in the MC1R gene necessary, but not always sufficient, for red hair production.
Origins
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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