Жылқы түсінің сирек кездесетін түрлеріне жауапты қарапайым аллель

Simple dominant allele responsible for a number of rare horse coat colors

The champagne gene is a simple dominant allele responsible for a number of rare horse coat colors. The most distinctive traits of horses with the champagne gene are the hazel eyes and pinkish, freckled skin, which are bright blue and bright pink at birth, respectively. The coat color is also affected: any hairs that would have been red are gold, and any hairs that would have been black are chocolate brown. If a horse inherits the champagne gene from either or both parents, a coat that would otherwise be chestnut is instead gold champagne, with bay corresponding to amber champagne, seal brown to sable champagne, and black to classic champagne. A horse must have at least one champagne parent to inherit the champagne gene, for which there is now a DNA test. Unlike the genes underlying tobiano, dominant white, frame overo spotting and the Leopard complex common to the Appaloosa, the champagne gene does not affect the location of pigment producing cells in the skin. Nor does the champagne gene remove all pigment from the skin and hair, as in albinism. Instead, the champagne gene produces traits known as hypomelanism, or dilution. Champagne is not associated with any health defects. Other dilution genes in horses include the Cream gene, Dun gene, Pearl gene and Silver dapple gene. Horses affected by these genes can sometimes be confused with champagnes, but champagnes are genetically distinct. Champagnes are not palominos, buckskins, or grullos, nor does the word champagne indicate that a horse is a shiny or light shade of another coat color. This gene and the associated coat colors are only known in American breeds, especially the American Cream Draft, Tennessee Walker, American Saddlebred and Missouri Fox Trotter.

The presence of other coat color modifying alleles has no effect on whether or not a horse has the champagne trait. However, different traits may interact; they may suppress, enhance, obscure or cancel out various tell tale clues to the genetic identity of a coat color. Coat colors involving multiple genes often have an unexpected appearance and unique terminology. This type of genetic interaction is called epistasis. Horses with both the champagne gene and the cream gene are the most common combination. The cream gene is responsible for the palomino, buckskin and cremello coat colors, and is a dose dependent or incomplete dominant, meaning that a horse with only one copy is visibly different from a horse with two copies of the gene. A single copy of the cream gene dilutes red pigment in the coat to gold or yellow, and has a slight effect on the skin and eye color. The black pigment is lightened little, if at all. Two copies of the cream gene dilute both red and black pigments in the hair to cream or ivory, dilute the skin to a rosy pink and the eyes to pale blue. The cream gene and champagne gene have an additive or enhancing interaction. Horses with the champagne gene and a single cream gene typically have lighter yellowish or blue eyes and paler, more faintly freckled skin. Gold cream or Ivory champagne refers to an otherwise chestnut coat affected by the champagne gene and a single copy of the cream gene. The mane, tail, and coat of gold creams are typically ivory and difficult to distinguish from cremello, other than by the skin and eyes. Amber cream, similarly, is an otherwise bay coat affected by the champagne gene and a single copy of the cream gene. The terms "cremello champagne", "perlino champagne" and so forth are also acceptable. Horses with both the champagne gene and the dun gene are also well recorded. The dun gene is responsible for flat, diluted coat colors and vivid primitive markings. Bay dun is thought to be the wildtype horse coat color. Dun does not affect skin or eye color, but dilutes red pigment to yellow and black pigment to slate gray. Champagne horses with the dun gene will have slightly further diluted coats compared to non dun champagnes, and will always exhibit striking primitive markings, such as a dorsal stripe and zebra like stripes on the legs. Naming schemes are much the same as with champagne cream combinations. Champagne dun combinations retain their champagne eye and skin traits. The coats are distinguishable from non champagne duns in that they are several shades lighter, black pigment is chocolate rather than slate, and they may exhibit a sheen. The coats are distinguishable from non dun champagnes in the presence of primitive markings and a flatter tone. Gold dun refers to an otherwise chestnut coat affected by both the champagne gene and dun gene. The mane and tail may be ivory or self colored; the body coat ranges from a warm cream to apricot color with primitive markings a shade darker. The coat is substantially paler and more "yellow" than that of a chestnut dun, and flatter than that of a gold champagne. Amber dun refers to an otherwise bay coat affected by both the champagne gene and dun gene. Silvers vary tremendously in shade and so defining a "typical" example is difficult. Amber silver refers to an otherwise bay coat affected by both the champagne gene and silver gene. The darkest examples resemble classic champagnes with a silvery mane and tail. The palest are a very pale pewter. Some have warm chocolate tones, others do not. The champagne gene, in combination with some white patterning genes, can also produce unexpected phenotypes. Horses with the leopard gene or Appaloosas exhibit starkly mottled skin around the muzzle, eyes, anus and sheath or udder. Most commonly, the mottling is blocky patches of normal, black skin and unpigmented pink. When a horse has both the leopard gene and the champagne gene, the champagne associated skin is present only where the skin would be otherwise black. In combination with gray, champagne produces very unusual coat behavior. Typically, gray horses are born a dark shade of their natural color, and begin to develop gray hairs around the eyes and muzzle. With each shed, the coat becomes lighter and lighter. Many older grays develop the "fleabitten" trait, in which small, interspersed flecks of red occur and often increase in density with age, even as the rest of the coat loses pigment. A few grays will also develop vitiligo in which the skin also progressively loses pigment. When a horse carries both gray and champagne, additional traits occur: Gray champagnes are born with darker coats than the usual champagne foal, but still exhibiting the expected bright blue eyes and pink skin. The freckling that develops on the skin is also exceptionally dark and dense. Gray champagnes appear more likely to experience vitiligo.

Many coat color modifying genes affect the skin and eyes as well as the coat color. Several of these may be confused with champagne. Today, when the visible cues are insufficient, horses can be DNA tested for the champagne gene, Cream gene, Pearl gene, and Silver dapple gene. Palomino or Chestnut vs. Gold champagne: The most common confusion, as both of these genetically distinct coat colors feature a gold or yellow coat and ivory or cream mane and tail. As adults, the pinkish freckled skin and hazel eyes indicate gold champagne, while gray or black skin and light or dark brown eyes indicate palomino. At birth, palominos may have pink skin and blue or grey eyes, however these darken within days or weeks. Occasionally, chestnuts are also born with blue eyes and pink skin, and as gold champagnes often have chestnut colored foal coats, the two can be difficult to distinguish. Again, the skin and eyes of the chestnut will darken quickly. In all cases, pedigrees can provide important information. Palominos will have a parent that is palomino, buckskin, smoky black, or blue eyed cream. Champagnes will have a champagne parent. Buckskin and Bay dun vs. Amber champagne: All three of these genetically distinct coat colors feature a lighter bronze or tan coat with darker points. As adults, the pinkish freckled skin and hazel eyes indicate amber champagne, while gray or black skin and light or dark brown eyes indicate buckskin or bay dun. Duns do not exhibit unusually colored skin, though buckskins, like palominos, may be born with blue eyes that darken within days or weeks. Bay dun horses also exhibit primitive markings, especially a dorsal stripe, though amber duns will also possess these marks. The eyes and skin remain the best identifying feature. Buckskins, like palominos, will a parent that is palomino, buckskin, smoky black, or blue eyed cream. Bay duns will have a parent that is bay dun, red dun, or grullo. Champagnes will have a champagne parent. Grullo vs. Classic champagne or Sable champagne: Classic and sable champagnes are difficult to distinguish without a DNA test. Grullos and classic champagnes are both dilutions of the black coat, and typically have black or dark points and dove gray coats. However, Grullos, in absence of any other dilution factors, are not born with pink skin and blue eyes, while champagnes always have these traits. As adults, grullos will retain their dark brown eyes and black skin, while champagnes have pinkish freckled skin and hazel eyes. Grullos, like all duns, will possess primitive markings, and their coats are typically a cooler, slate shade, while classic and sable champagnes are chocolate toned. The points and primitive markings on the grullo are black, while the points on classic and sable champagnes are brown. Grullos will have dun ancestry and champagnes will have champagne ancestry. Red dun vs. Dark gold champagne: Some gold champagnes have darker bodies and self colored manes and tails. These horses may resemble red duns, however red duns have distinct primitive markings and do not possess pinkish freckled skin or hazel eyes as adults, nor the bright pink skin and bright blue eyes of champagne foals. The champagne gene is also found in the Tennessee Walking Horse, American Saddlebred, Missouri Fox Trotter, Racking horse, Kentucky Mountain Saddle Horse, Spanish Mustang, American Quarter Horse, American Paint Horse, Appaloosa and Miniature horse breeds.

The champagne gene was located in 2008, but is not a new mutation. It is widespread among American horses, and has likely been present in the genepool for more than a century. The Palomino Horse Breeders Association (PHBA), which registers "palomino" horses based on appearance, includes allowances for freckle skinned and hazel eyed palominos. Furthermore, while the registry typically disallows horses with pink skin, it allows American Saddlebreds with skin of any color to be registered. The PHBA was incorporated in 1941. Further back, the foundation mare of the American Cream Draft horse breed, "Old Granny", was born around 1905 in Iowa. The superficial similarities between gold champagne and palomino, and amber champagne and buckskin, may account for the relatively recent identification of champagne as a separate trait. Gold champagnes were sometimes called "pumpkin skinned palomino." Classic champagnes, which lack the primitive markings of true duns, were similarly called "lilac duns." The mare that brought the champagne coat color family to the attention of modern researchers was a Tennessee Walking Horse named "Champagne Lady Diane" born in 1969. A classic champagne, Champagne Lady Diane was described as "a genetic color accident" after her hairs were sent to several universities, although current evidence suggests that the champagne gene predates Champagne Lady Diane. It was not until many years after the name "champagne" was ascribed to Champagne Lady Diane that the term appeared in scientific literature. It was first studied and described by Sponenberg and Bowling in 1996. They studied the ratio of champagne to non champagne offspring of champagne horses, and designated the causal mutation as the dominant Ch allele on the hypothetical Champagne locus.

The champagne locus is on exon 2 of the SLC36A1 gene, which is on chromosome 14 (ECA14); a single nucleotide polymorphism (SNP) exchanges a C for a G at base 76 (c.188C>G) resulting in a missense mutation. On a protein level, this SNP is predicted to result in the replacement of a threonine with arginine at amino acid 63 (T63R). SLC36A1 is not associated with pigmentation phenotypes in other species, and its role in most tissues is poorly understood. SLC36A1 is a member of a loosely united group of over 300 proteins responsible for active transport and facilitated diffusion called the Solute carrier family. Other members of this family include SLC45A2, which is responsible for pigmentation variations of many types in humans, as well as the cream coat color in horses; and SLC24A5, which is responsible for the Golden dilution in mice. Dilution genes such as champagne and cream affect the nature or density of the pigments produced by melanocytes. On the other hand, genes in horses which produce white spotting, such as Frame and Sabino1, interrupt or limit the migration of melanocytes from the neural crest. In other words, the skin, eyes, and hair of horses with the champagne mutation do not lack melanocytes, melanosomes, or melanins, but rather exhibit hypomelanism. However, the specific role of SLC36A1 in pigmentation and how the champagne coat colors are created on a molecular level is not known. The researchers who identified the mutation in 2008 suggested that melanosome pH may be affected, which in turn might affect the processing of tyrosine, a critical element of melanogenesis. There are two alleles in this series: the recessive, wildtype allele ch and the dominant CH. The DNA test for champagne detects the c.188C>G mutation on SLC36A1.