Question:

If you have red hair what is the probability that your kids will have red hair?

Answer:

If the parents both have a functioning and a mutant version of the MC1R gene that causes red hair, they are said to be carriers and there is a 1 in 4 chance of them having a child who is a redhead.

More Info:

In genetics, a locus (plural loci) is the specific location of a gene or DNA sequence on a chromosome. A variant of the similar DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map. Gene mapping is the process of determining the locus for a particular biological trait. Diploid and polyploid cells whose chromosomes have the same allele of a given gene at some locus are called homozygous with respect to that gene, while those that have different alleles of a given gene at a locus, are called heterozygous with respect to that gene.][ The chromosomal locus of a gene might be written "6p21.3". Because "21" refers to "region 2, band 1" this is not read as "twenty-one," rather it is read as "two one." So the entire locus is "six P two one point three." A range of locales is specified in a similar way. For example, the locus of gene OCA1 may be written "11q1.4-q2.1", meaning it is on the long arm of chromosome 11, somewhere in the range from sub-band 4 of band 1 to sub-band 1 of band 2. The ends of a chromosome are labeled "pter" and "qter", and so "2qter" refers to the telomere of the long arm of chromosome 2. A centisome (not to be confused with a centrosome) is defined as 1% of a chromosome length.
Red hair occurs naturally on approximately 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 in people with two copies of a recessive gene on chromosome 16 which causes a mutation in 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. The term redhead (originally redd hede) has been in use since at least 1510. It is associated with fair skin color, lighter eye colors (gray, blue, green, and hazel), freckles, and sensitivity to ultraviolet light. Cultural reactions have varied from ridicule to admiration; many common stereotypes exist regarding redheads and they are often portrayed as fiery-tempered. Several accounts by Greek writers mention redheaded people. A fragment by the poet Xenophanes describes the Thracians as blue-eyed and red haired. Herodotus described the Budini people as being predominantly red haired. Dio Cassius described Boudica, Queen of the Iceni, of the ancient Britons, to be "tall and terrifying in appearance... a great mass of red hair... over her shoulders." The Roman historian Tacitus commented on the "red hair and large limbs of the inhabitants of Caledonia", which he connected with some red haired Gaulish tribes of Germanic and Belgic relation. 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. Red hair is also found amongst Polynesians, and is especially common in some tribes and family groups. In Polynesian culture red hair has traditionally been seen as a sign of descent from high ranking ancestors and a mark of rulership. Today, red hair is most commonly found at the northern and western fringes of Europe; it is associated particularly with the people located in the British Isles (although Victorian era ethnographers claimed that the Udmurt people of the Volga were "the most red-headed men in the world"). Redheads are common among Germanic and Celtic peoples. Redheads constitute approximately 4% of the European population. Scotland has the highest proportion of redheads; 13% of the population has red hair and approximately 40% carries the recessive redhead gene. Ireland has the second highest percentage; as many as 10% of the Irish population has red, auburn, or strawberry blond hair. It is thought that up to 46% of the Irish population carries the recessive redhead gene.][ A 1956 study of hair colour amongst British army recruits also found high levels of red hair in Wales and the English Border counties. Red hair is also fairly common amongst the Ashkenazi Jewish populations, possibly because of the influx of European DNA over a period of centuries. In European culture, prior to the 20th century, red hair was often seen as a stereotypically Jewish trait: during the Spanish Inquisition, all those with red hair were identified as Jewish. In Italy, red hair was associated with Italian Jews, and Judas was traditionally depicted as red-haired in Italian and Spanish art. Writers from Shakespeare to Dickens would identify Jewish characters by giving them red hair. The stereotype that red hair is Jewish remains in parts of Eastern Europe and Russia. In the United States, it is estimated that 2–6% of the population has red hair. This would give the U.S. the largest population of redheads in the world, at 6 to 18 million, compared to approximately 650,000 in Scotland and 420,000 in Ireland.][ The Berber populations of Morocco and northern Algeria have occasional redheads. Red hair frequency is especially significant among the Kabyles from Algeria, where it reaches 4%. The Queen of Morocco, Lalla Salma wife of king Mohammed VI, has red hair. Abd ar-Rahman I also had red hair, his mother being a Christian Berber slave. In Asia, red hair can be found in the Levant (such as Syria, Lebanon, Jordan, Iraq, Israel and Palestine), in Turkey, the Caucasus, Central Asia, and amongst those of Indo-Iranian descent, such as the Persians, Tajiks, Lurs, Kurds, Pashtuns, Nuristanis and Dards. Emigration from Eurasia and North Africa added to the population of red haired humans in the Americas, Australia, New Zealand and Southern Africa. 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 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. The alleles that code for red hair occur close to the alleles that affect skin color, so it seems that the phenotypic expression for lighter skin and red hair are interrelated. 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. 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. In species other than primates, red hair has different genetic origins and mechanisms. 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. 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. Melanin in the skin aids UV tolerance through suntanning, but fair-skinned persons lack the levels of melanin needed to prevent UV-induced DNA-damage. Studies have shown that red hair alleles in MC1R increase freckling and decrease tanning ability. It has been found that Europeans who are heterozygous for red hair exhibit increased sensitivity to UV radiation. Red hair and its relationship to UV sensitivity are of interest to many melanoma researchers. Sunshine can both be good and bad for a person's health and the different alleles on MC1R represent these adaptations. It also has been shown that individuals with pale skin are highly susceptible to a variety of skin cancers such as melanoma, basal cell carcinoma, and squamous cell carcinoma. Two studies have demonstrated that people with red hair have different sensitivity to pain compared to people with other hair colors. One study found that people with red hair are more sensitive to thermal pain (associated with naturally occurring low vitamin K levels), while another study concluded that redheads are less sensitive to pain from multiple modalities, including noxious stimuli such as electrically induced pain. Researchers have found that people with red hair require greater amounts of anesthetic. Other research publications have concluded that women with naturally red hair require less of the painkiller pentazocine than do either women of other hair colors or men of any hair color. A study showed women with red hair had a greater analgesic response to that particular pain medication than men. A follow-up study by the same group showed that men and women with red hair had a greater analgesic response to morphine-6-glucuronide. The unexpected relationship of hair color to pain tolerance appears to exist because redheads have a mutation in a hormone receptor that can apparently respond to at least two types of hormones: the pigmentation driving melanocyte-stimulating hormone (MSH), and the pain relieving endorphins. (Both derive from the same precursor molecule, POMC, and are structurally similar.) Specifically, redheads have a mutated melanocortin-1 receptor (MC1R) gene that produces an altered receptor for MSH. Melanocytes, the cells that produce pigment in skin and hair, use the MC1R to recognize and respond to MSH from the anterior pituitary gland. Melanocyte-stimulating hormone normally stimulates melanocytes to make black eumelanin, but if the melanocytes have a mutated receptor, they will make reddish pheomelanin instead. MC1R also occurs in the brain, where it is one of a large set of POMC-related receptors that are apparently involved not only in responding to MSH, but also in responses to endorphins and possibly other POMC-derived hormones. Though the details are not clearly understood, it appears that there is some "cross talk" between the POMC hormones that may explain the link between red hair and pain tolerance. There is little or no evidence to support the belief that people with red hair have a higher chance than people with other hair colors to hemorrhage or suffer other bleeding complications. One study, however, reports a link between red hair and a higher rate of bruising. Most red hair is caused by the MC1R gene and is non-pathological. However, in rare cases red hair can be associated with disease or genetic disorder: In various times and cultures, red hair has been prized, feared, and ridiculed. A common belief about redheads is that they have fiery tempers and sharp tongues. In Anne of Green Gables, a character says of Anne Shirley, the redheaded heroine, that "her temper matches her hair", while in The Catcher in the Rye, Holden Caulfield remarks that "People with red hair are supposed to get mad very easily, but Allie [his dead brother] never did, and he had very red hair." During the early stages of modern medicine, red hair was thought to be a sign of a sanguine temperament. In the Indian medicinal practice of Ayurveda, redheads are seen as most likely to have a Pitta temperament. Another belief is that redheads are highly sexed; for example, Jonathan Swift satirizes redhead stereotypes in part four of Gulliver's Travels, "A Voyage to the Country of the Houyhnhnms," when he writes that: "It is observed that the red-haired of both sexes are more libidinous and mischievous than the rest, whom yet they much exceed in strength and activity." Swift goes on to write that: "...neither was the hair of this brute [a Yahoo] of a red colour (which might have been some excuse for an appetite a little irregular) but black as a sloe..." Such beliefs were given a veneer of scientific credibility in the 19th century by Cesare Lombroso and Guglielmo Ferrero. They concluded that red hair was associated with crimes of lust, and claimed that 48% of "criminal women" were redheads. In the novel and film Red-Headed Woman, the titular protagonist is a sexually aggressive home-wrecker who frequently throws violent temper tantrums. Queen Elizabeth I of England was a redhead, and during the Elizabethan era in England, red hair was fashionable for women. In modern times, red hair is subject to fashion trends; celebrities such as Nicole Kidman, Alyson Hannigan, Marcia Cross, Christina Hendricks, Emma Stone and Geri Halliwell can boost sales of red hair dye.][ Sometimes, red hair darkens as people get older, becoming a more brownish color or losing some of its vividness. This leads some to associate red hair with youthfulness, a quality that is generally considered desirable. In several countries such as India, Iran, Bangladesh and Pakistan, henna and saffron are used on hair to give it a bright red appearance. Many painters have exhibited a fascination with red hair. The color "titian" takes its name from Titian, who often painted women with red hair. Early Renaissance artist Sandro Botticelli's famous painting The Birth of Venus depicts the mythological goddess Venus as a redhead. Other painters notable for their redheads include the Pre-Raphaelites, Edmund Leighton, Modigliani, and Gustav Klimt. Sir Arthur Conan Doyle's story The Red-Headed League involves a man who is asked to become a member of a mysterious group of red-headed people. The 1943 film DuBarry Was a Lady featured red-heads Lucille Ball and Red Skelton in Technicolor. Red hair was thought to be a mark of a beastly sexual desire and moral degeneration. A savage red-haired man is portrayed in the fable by Grimm brothers (Der Eisenhans) as the spirit of the forest of iron. Theophilus Presbyter describes how the blood of a red-haired young man is necessary to create gold from copper, in a mixture with the ashes of a basilisk. Montague Summers, in his translation of the Malleus Maleficarum, notes that red hair and green eyes were thought to be the sign of a witch, a werewolf or a vampire during the Middle Ages; In his book "I Say No" Wilkie Collins (1885) wrote "The prejudice against habitual silence, among the lower order of the people, is almost as inveterate as the prejudice against red hair." In modern-day UK, the words "ginger" or "ginga" are sometimes used to describe red-headed people (and are at times considered insulting), with terms such as "gingerphobia" (hatred towards redheads) or "gingerism" (prejudice against redheads) used by the British media. In Britain, redheads are also sometimes referred to disparagingly as "carrot tops" and "carrot heads". (The comedian "Carrot Top" uses this stage name.) "Gingerism" has been compared to racism, although this is widely disputed, and bodies such as the UK Commission for Racial Equality do not monitor cases of discrimination and hate crimes against redheads. A UK woman recently won an award from a tribunal after being sexually harassed and receiving abuse because of her red hair; a family in Newcastle upon Tyne, England, was forced to move twice after being targeted for abuse and hate crime on account of their red hair; and in 2003, a 20-year-old was stabbed in the back for "being ginger". In May 2009, a British schoolboy committed suicide after being bullied for having red hair. The British singer Mick Hucknall, who says that he has repeatedly faced prejudice or been described as ugly on account of his hair color, argues that Gingerism should be described as a form of racism. This prejudice has been satirised on a number of TV shows. The British comedian Catherine Tate (herself a redhead) appeared as a red-haired character in a running sketch of her series The Catherine Tate Show. The sketch saw fictional character Sandra Kemp, who was forced to seek solace in a refuge for ginger people because they had been ostracised from society. The British comedy Bo' Selecta! (starring redhead Leigh Francis) featured a spoof documentary which involved a caricature of Mick Hucknall presenting a show in which celebrities (played by themselves) dyed their hair red for a day and went about daily life being insulted by people. The pejorative use of the word "ginger" and related discrimination was used to illustrate a point about racism and prejudice in the "Ginger Kids", "Le Petit Tourette", "It's a Jersey Thing" and "Fatbeard" episodes of South Park. In the United States, film and television programmes often portray school bullies as having red hair; for example, Scut Farkus from A Christmas Story or the O'Doyle family in the movie Billy Madison. The bully character Caruso in Everybody Hates Chris is a redhead. However, children with red hair are often themselves targeted by bullies; "Somebody with ginger hair will stand out from the crowd," says anti-bullying expert Louise Burfitt-Dons. In Australian slang, redheads are often nicknamed "Blue" or "Bluey". More recently, they have been referred to as "rangas" (a word derived from the red-haired ape, the orangutan), sometimes with derogatory connotations. The word "rufus" has been used in both Australian and British slang to refer to red-headed people; based on a variant of rufous, a reddish-brown colour. In November 2008 social networking website Facebook received criticism after a 'Kick a Ginger' group, which aimed to establish a "National Kick a Ginger Day" on November 20, acquired almost 5,000 members. A 14-year-old boy from Vancouver who ran the Facebook group was subjected to an investigation by the Royal Canadian Mounted Police for possible hate crimes. In December 2009 British supermarket chain Tesco withdrew a Christmas card which had the image of a child with red hair sitting on the lap of Santa Claus, and the words: "Santa loves all kids. Even ginger ones" after customers complained the card was offensive. In October 2010, Harriet Harman, the former Equality Minister in the British government under Labour, faced accusations of prejudice, after she described the red-haired Treasury secretary Danny Alexander as a "ginger rodent". Alexander responded to the insult by stating that he was "proud to be ginger". Harman was subsequently forced to apologise for the comment, after facing criticism for prejudice against a minority group. In September 2011, Cryos International, one of the world's largest sperm banks, announced that it would no longer accept donations from red-haired men due to low demand from women seeking artificial insemination. The term ang mo (Chinese: ; pinyin: hóng máo; Pe̍h-ōe-jī: âng-mo͘) in Hokkien (Min Nan) Chinese means "red-haired", and is used in Malaysia and Singapore to refer to English people. The epithet is sometimes rendered as ang mo kui () meaning "red-haired devil", similar to the Cantonese term gweilo ("foreign devil"). Thus it is viewed as racist and derogatory by some people. Others, however, maintain it is acceptable. Despite this ambiguity, it is a widely used term. It appears, for instance, in Singaporean newspapers such as The Straits Times, and in television programmes and films. The Chinese characters for ang mo are the same as those in the historical Japanese term Kōmō (), which was used during the Edo period (1603–1868) as an epithet for Dutch or Northern European people. It primarily referred to Dutch traders who were the only Europeans allowed to trade with Japan during Sakoku, its 200-year period of isolation. Redheadday is the name of a Dutch festival that takes place each first weekend of September in the city of Breda, the Netherlands. The two-day festival is a gathering of people with natural red hair, but is also focused on art related to the color red. Activities during the festival include lectures, workshops and demonstrations. In the Iliad, Achilles' hair is described as ξανθῆς, usually translated as blonde, or golden but sometimes as red or tawny. His son Neoptolemus also bears the name Pyrrhus, a possible reference to his own red hair. The Norse god Thor is usually described as having red hair. The Hebrew word usually translated "ruddy" or "reddish-brown" (admoni (ואדמני), from the root ADM (אדם, see also Adam and Edom)) was used to describe both Esau and David. Despite the fact hair colour is not mentioned in the passages, the descriptions led to a later Ashkenazi tradition that David and Esau were a red-head.][ Early artistic representations of Mary Magdalene usually depict her as having long flowing red hair, although a description of her hair color was never mentioned in the Bible, and it is possible the color is an effect caused by pigment degradation in the ancient paint. Red hair dyeing is sometimes practised in Islam, because it is reported that Muhammad had red hair. Judas Iscariot is also represented with red hair in Spanish culture and in the works of William Shakespeare, reinforcing the negative stereotype. There is a tradition amongst astrologers that the planet Mars ("the red planet") is more likely to be rising above the eastern horizon (on or near the astrological Ascendant, which supposedly influences a person's appearance) at the time of the birth of a red haired person than for the population in general.
Asp294His (rs1805009) is a single nucleotide polymorphism (SNP) in the MC1R gene and it is associated with red hair and light skin type. Other SNPs in the gene, Arg151Cys and Arg160Trp, are also associated with red hair.
In genetics, a missense mutation (a type of nonsynonymous mutation) is a point mutation in which a single nucleotide change results in a codon that codes for a different amino acid (mutations that change an amino acid to a stop codon are considered nonsense mutations, rather than missense mutations). This can render the resulting protein nonfunctional . Such mutations are responsible for diseases such as Epidermolysis bullosa, sickle-cell disease, and SOD1 mediated ALS (Boillée 2006, p. 39). For example, in the most common variant of sickle-cell disease, the 20th nucleotide of the gene for the beta chain of hemoglobin found on chromosome 11 is erroneously changed from the codon GAG (for glutamic acid) to GUG (which codes valine). Thus, the 6th amino acid is incorrectly substituted (after the initial methionine amino acid is removed) and the protein is significantly altered to cause the sickle-cell disease. Not all missense mutations lead to appreciable protein changes. An amino acid may be replaced by an amino acid of very similar chemical properties, in which case, the protein may still function normally; this is termed a neutral, "quiet", "silent" or conservative mutation. Alternatively, the amino acid substitution could occur in a region of the protein which does not significantly affect the protein secondary structure or function. When an amino acid may be encoded by more than one codon (so-called "degenerate coding") a mutation in a codon may not produce any change in translation; this would be a synonymous mutation (a form of silent mutation) and not a missense mutation. A special type of missense mutation that results in truncation of code is the nonsense mutation. Cancer associated missense mutations can lead to drastic destabilisation of the resulting protein . A novel method to screen for such changes was proposed recently, namely Fast parallel proteolysis (FASTpp) .
Agouti signalling peptide, a product of the Agouti gene, is a peptide consisting of 131 amino acids. Its discovery was published in 1994 in the scientific journal Nature where its functional properties were described. It acts as an inverse agonist at melanocortin receptors, specifically, MC1. It is produced by the Agouti gene ASIP. In mice, the agouti gene encodes a paracrine signalling molecule that causes hair follicle melanocytes to synthesize pheomelanin, a yellow pigment, instead of the black or brown pigment, eumelanin. Pleiotropic effects of constitutive expression of the mouse gene include adult-onset obesity, increased tumor susceptibility, and premature infertility. This gene is highly similar to the mouse gene and encodes a secreted protein that may (1) affect the quality of hair pigmentation, (2) act as an inverse agonist of alpha-melanocyte-stimulating hormone, (3) play a role in neuroendocrine aspects of melanocortin action, and (4) have a functional role in regulating lipid metabolism in adipocytes. This article incorporates text from the United States National Library of Medicine, which is in the public domain.
The melanocortin 1 receptor (MC1R), also known as melanocyte-stimulating hormone receptor (MSHR), melanin-activating peptide receptor, or melanotropin receptor, is a G protein-coupled receptor which binds to a class of pituitary peptide hormones known as the melanocortins, which include adrenocorticotropic hormone (ACTH) and the different forms of melanocyte-stimulating hormone (MSH). MC1R is one of the key proteins involved in regulating mammalian skin and hair color. It is located on the plasma membrane of specialized cells known as melanocytes, which produce the pigment melanin through a process referred to as melanogenesis. It works by controlling the type of melanin being produced and its activation causes the melanocyte to switch from generating the yellow or red phaeomelanin by default to the brown or black eumelanin in replacement. The MC1R protein lies within the cell membrane, and is signalled by melanocyte-stimulating hormone (MSH) released by the pituitary gland. When activated by one of the variants of MSH, typically α-MSH, MC1R initiates a complex signaling cascade that leads to the production of the brown or black pigment eumelanin. In contrast, the receptor can also be antagonized by agouti signalling peptide (ASIP), which reverts the cell back to producing the yellow or red phaeomelanin. The pulsatile nature of ASIP signalling through MC1R produces the characteristic yellow and black agouti banding pattern observed on most mammalian hair. In some species ASIP signaling is not of a pulsative nature, but is limited to certain regions. This is especially conspicuous in horses, where a bay horse has black legs, mane and tail, but a reddish body. A notable exception to this is human hair, which is neither banded nor particoloured, and thus is thought to be regulated by α-MSH signaling through MC1R exclusively. In the United States, approximately 25 percent of the population are carrying the mutated Melanocortin 1 Receptor that causes red hair. The chance of two people having a child with red hair is 1-3 in every hundred (approximately 1 in 64). In mutant yellow-orange mice and human redheads, both with non-functional MC1R, show that both genotypes display reduced sensitivity to noxious stimuli and increased analgesic responsiveness to morphine-metabolite analgetics. These observations suggests a role for mammalian MC1R outside the pigment cell, though the exact mechanism through which the protein can modulate pain sensation is not known. People with freckles and no red hair have an 85 percent chance of carrying the defective MC1R gene that is connected to red hair. People with no freckles and no red hair have an 18 percent chance of carrying the defective MC1R gene linked to red hair. MC1R has a slightly different function in cold-blooded animals such as fish, amphibians and reptiles. Here α-MSH activation of MC1R results in the dispersion of eumelanin filled melanosomes throughout the interior of pigment cells (called melanophores). This gives the skin of the animal a darker hue and often occurs in response to changes in mood or environment. Such a physiological color change implicates MC1R as a key mediator of adaptive cryptic coloration. The role of ASIP binding to MC1R in regulating this adaptation is unclear, however in teleost fish at least, functional antagonism is provided by melanin concentrating hormone. This signals through its receptor to aggregate the melanosomes towards a small area in the centre of the melanophore, resulting in the animal having a lighter overall appearance. Cephalopods generate a similar, albeit more dramatic, pigmentary effect using muscles to rapidly stretch and relax their pigmented chromatophores. MC1R does not appear to play a role in the rapid and spectacular colour changes observed in these invertebrates. MC1R gene expression is regulated by the microphthalmia-associated transcription factor (MITF). Mutations of the MC1R gene can either create a receptor that constantly signals, even when not stimulated, or can lower the receptor's activity. Alleles for constitutively active MC1R are inherited dominantly and result in a black coat colour, while alleles for dysfunctional MC1R are recessive and result in a light coat colour. Variants of MC1R associated with black, red/yellow and white/cream coat colors in numerous animal species have been reported, including (but not limited to): A study on unrelated British and Irish individuals demonstrated that over 80% of people with red hair and/or fair skin that tans poorly have a dysfunctional variant of the MC1R gene. This is compared to less than 20% in brown or black haired people, and less than 4% in people showing a good tanning response. The Out-of-Africa model proposes that modern humans originated in Africa and migrated north to populate Europe and Asia. It is most likely that these migrants had a functional MC1R variant and, accordingly, dark hair and skin as displayed by indigenous Africans today. As humans migrated north, the absence of high levels of solar radiation in northern Europe and Asia relaxed the selective pressure on active MC1R, allowing the gene to mutate into dysfunctional variants without reproductive penalty, then propagate by genetic drift. Studies show the MC1R Arg163Gln allelle has a high frequency in East Asia and may be part of the evolution of light skin in East Asian populations. There is no evidence for positive selection of MC1R allelles in Europe and no evidence of an association between MC1R and the evolution of light skin in European populations.
The melanocyte-stimulating hormones (collectively referred to as MSH or intermedins) are a class of peptide hormones that are produced by cells in the intermediate lobe of the pituitary gland. Synthetic analogs of these naturally occurring hormones have also been developed and researched. They stimulate the production and release of melanin (melanogenesis) by melanocytes in skin and hair. MSH signals to the brain have effects on appetite and sexual arousal. In some animals (such as the claw-toed frog Xenopus laevis) production of MSH is increased when the animal is in a dark location. This causes pigment to be dispersed in pigment cells in the toad's skin, making it become darker, and harder for predators to spot. The pigment cells are called melanophores and therefore, in amphibians, the hormone is often called melanophore-stimulating hormone. An increase in MSH will cause a darkening in humans too. Melanocyte-stimulating hormone increases in humans during pregnancy. This, along with increased estrogens, causes increased pigmentation in pregnant women. Cushing's syndrome due to excess adrenocorticotropic hormone (ACTH) may also result in hyperpigmentation, such as acanthosis nigricans in the axilla. Most people with primary Addison's have darkening (hyperpigmentation) of the skin, including areas not exposed to the sun; characteristic sites are skin creases (e.g. of the hands), nipple, and the inside of the cheek (buccal mucosa), new scars become hyperpigmented, whereas older ones do not darken. This occurs because melanocyte-stimulating hormone (MSH) and adrenocorticotropic hormone (ACTH) share the same precursor molecule, Pro-opiomelanocortin (POMC). Different levels of MSH are not the major cause of racial variation in skin colour. However, in many red headed people, and other people who do not tan well, there are variations in their hormone receptors, causing them to not respond to MSH in the blood. See melanocortin receptor for more information. Melanocyte-stimulating hormone belongs to a group called the melanocortins. This group includes ACTH, alpha-melanocyte-stimulating hormone (α-MSH), beta-melanocyte-stimulating hormone (β-MSH) and gamma-melanocyte-stimulating hormone (γ-MSH); these peptides are all cleavage products of a large precursor peptide called pro-opiomelanocortin (POMC). α-MSH is the most important melanocortin for pigmentation. The different melanocyte-stimulating hormones have the following amino acid sequences: Synthetic analogs of α-MSH have been developed for human use. Two of the better known are afamelanotide (melanotan-1) in testing by Clinuvel Pharmaceuticals in Australia and bremelanotide by Palatin Technologies, a New Jersey company. Testis: testosterone  AMH  inhibin Ovary: estradiol  progesterone  activin and inhibin  relaxin (pregnancy) Thymus: Thymosin (Thymosin α1, Thymosin beta)  Thymopoietin  Thymulin Digestive system: Stomach: gastrin  ghrelin  Duodenum: CCK  Incretins (GIP, GLP-1)   secretin  motilin  VIP  Ileum: enteroglucagon  peptide YY  Liver/other: Insulin-like growth factor (IGF-1, IGF-2) Adipose tissue: leptin  adiponectin  resistin Skeleton: Osteocalcin Kidney: JGA (renin)  peritubular cells (EPO)  calcitriol  prostaglandin M: END anat/phys/devp/horm noco (d)/cong/tumr, sysi/epon proc, drug (A10/H1/H2/H3/H5) Dopamine M: PNS anat (h/r/t/c/b/l/s/a)/phys (r)/devp/prot/nttr/nttm/ntrp noco/auto/cong/tumr, sysi/epon, injr proc, drug (N1B)

The melanocortin 1 receptor (MC1R), also known as melanocyte-stimulating hormone receptor (MSHR), melanin-activating peptide receptor, or melanotropin receptor, is a G protein-coupled receptor which binds to a class of pituitary peptide hormones known as the melanocortins, which include adrenocorticotropic hormone (ACTH) and the different forms of melanocyte-stimulating hormone (MSH). MC1R is one of the key proteins involved in regulating mammalian skin and hair color. It is located on the plasma membrane of specialized cells known as melanocytes, which produce the pigment melanin through a process referred to as melanogenesis. It works by controlling the type of melanin being produced and its activation causes the melanocyte to switch from generating the yellow or red phaeomelanin by default to the brown or black eumelanin in replacement.

Hair

Hair color is the pigmentation of hair follicles due to two types of melanin: eumelanin and pheomelanin. Generally, if more eumelanin is present, the color of the hair is darker; if less eumelanin is present, the hair is lighter. Levels of melanin can vary over time causing a person's hair color to change, and it is possible to have hair follicles of more than one color.

Particular hair colors are associated with ethnic groups. The shades of human hair color are assessed using the Fischer–Saller scale. The Fischer–Saller scale, named after Eugen Fischer and Karl Saller, is used in physical anthropology and medicine to determine the shades of hair color. The scale uses the following designations: A (light blond), B to E (blond), F to L (blond), M to O (dark blond), P to T (brown), U to Y (dark brown/black) and Roman numerals I to IV (red) and V to VI (red blond). See also the Martin–Schultz scale for eye color.

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Hair color is the pigmentation of hair follicles due to two types of melanin: eumelanin and pheomelanin. Generally, if more eumelanin is present, the color of the hair is darker; if less eumelanin is present, the hair is lighter. Levels of melanin can vary over time causing a person's hair color to change, and it is possible to have hair follicles of more than one color.

Particular hair colors are associated with ethnic groups. The shades of human hair color are assessed using the Fischer–Saller scale. The Fischer–Saller scale, named after Eugen Fischer and Karl Saller, is used in physical anthropology and medicine to determine the shades of hair color. The scale uses the following designations: A (light blond), B to E (blond), F to L (blond), M to O (dark blond), P to T (brown), U to Y (dark brown/black) and Roman numerals I to IV (red) and V to VI (red blond). See also the Martin–Schultz scale for eye color.

Biology

Red hair occurs naturally on approximately 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 in people with two copies of a recessive gene on chromosome 16 which causes a mutation in 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. The term redhead (originally redd hede) has been in use since at least 1510. It is associated with fair skin color, lighter eye colors (gray, blue, green, and hazel), freckles, and sensitivity to ultraviolet light.

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