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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.
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.Red hair (or ginger 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.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.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.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. concluded that red hair is not the result of positive selection but of a lack of negative selection.In the United States, it is estimated that 2–6% of the population has red hair. In Asia, red hair has been found among the ancient Tocharians, who occupied the Tarim Basin in what is now the northwesternmost province of China.Caucasian Tarim mummies have been found with red hair dating to the 2nd millennium BC.In species other than primates, red hair has different genetic origins and mechanisms.