"THE SCIENCE BEHIND REDHEAD"

BIOLOGY & STYLE

"THE SCIENCE BEHIND REDHEAD"

 To Celebrate The Redhead Day

“While the rest of the species is descended from apes, redheads are descended from cats.”  

 ― Mark Twain

 
Red hair is the rarest natural hair color in humans and today is celebrated in UK  "The National RedHead Day,"  commemorating this day  we have sought the the biological secret behind this hair color. Cultural reactions have varied from ridicule to admiration; many common stereotypes exist regarding redheads and they are often portrayed as fiery-tempered. The term redhead has been in use since at least 1510.

Red hair occurs naturally in 1–2% of the human population. It occurs more frequently (2–6%) in people of northern or western European ancestry, and less frequently in other populations. Red hair appears most commonly in people with two copies of a recessive allele on chromosome 16 which produces an altered version of the MC1R protein.

Red hair varies from a deep burgundy through burnt orange to bright copper. It is characterized by high levels of the reddish pigment pheomelanin and relatively low levels of the dark pigment eumelanin. It is associated with fair skin color, lighter eye colors (gray, blue, green, and hazel), freckles, and sensitivity to ultraviolet light.

Biochemistry and genetics

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 generally results in skin that is unable to tan. Because of the natural tanning reaction to the sun's ultraviolet light and high amounts of pheomelanin in the skin, freckles are a common but not all-inclusive feature of red-haired people. 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.

Evolution

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 is not the result of positive selection but of a lack of negative selection. In Africa, for example, red hair is selected against because high levels of sun harm untanned skin. However, in Northern Europe this does not happen, so redheads can become more common 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.

Extinction hoax

A 2007 report in The Courier-Mail, which cited the National Geographic magazine and unnamed "geneticists", said that red hair is likely to die out in the near future. Other blogs and news sources ran similar stories that attributed the research to the magazine or the "Oxford Hair Foundation". However, a HowStuffWorks article says that the foundation was funded by hair-dye maker Procter & Gamble, and that other experts had dismissed the research as either lacking in evidence or simply bogus. The National Geographic article in fact states "while redheads may decline, the potential for red isn't going away".

Red hair is caused by a relatively rare recessive gene, the expression of which can skip generations. It is not likely to disappear at any time in the foreseeable future.

SOURCE: wikipedia.org/wiki/Red_hair

Text is available under the Creative Commons Attribution-ShareAlike License  

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