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Roan is a coat color found in many animals, including horses, cattle, antelope, cat and dogs. It is defined generally as an even mixture of white and pigmented hairs that do not "gray out" or fade as the animal ages. [1] There are a variety of genetic conditions which produce the colors described as "roan" in various species.
A horse with intermixed white and colored hairs of any color is usually called a roan. [2] However, such mixtures, which can appear superficially similar, are caused by a number of separate genetic factors. Identifiable types of roans include true or classic roan, varnish roan, and rabicano, though other currently unknown factors may be responsible for ambiguous "roaning." [3] Gray horses, which become lighter as they age until their hair coat is nearly completely white, may be confused with roans when they are young. [2] Duns, which are solid-colored horses affected by the dun dilution factor on their bodies but with darker points, are also sometimes confused with roans, but they do not have the intermixed white and colored hairs of a roan.
Horses with the classic or true roan pattern may be any base color which is intermingled with unpigmented white hairs on the body. Except for white markings under the control of other genes, the head, mane, tail, and lower legs are dark. [2] Roan is a simple dominant trait symbolized by the Rn allele. [3] The University of California, Davis School of Veterinary Medicine's genetics services have developed a DNA test that uses genetic markers to indirectly determine the number of Rn or rn alleles a horse has. [3] The mutation responsible for true roan has not yet been identified exactly, but been assigned to equine chromosome 21 (ECA21) in the KIT sequence. [4] The overall effect is that of a silver or lightened appearance to the affected part of the coat. Descriptions of roan coat colors are as follows:
Any other coat color may also be affected by roaning. Few combinations have the same unique terminology applied to the common roan colors, although palomino roans are sometimes called honey roans.
A varnish roan is not a true roan; it is actually one of the leopard complex coat patterns associated with Appaloosa, Knabstrupper, Noriker horse and related breeds. Rabicano is a white pattern that falls into the category of roaning or scattered white hairs, the genetics of which are not yet fully understood. [2] Sometimes called ticking, rabicano is common even in breeds that do not have true or classic roan, including Arabians and Thoroughbreds. This pattern usually takes the form of scattered white hairs around the junction of the stifle and flank, and peculiar rings of white hairs near the base of the tail. This trait is called a coon tail or skunk tail. [5] Some forms of sabino, which is a pinto pattern, have roaning along the edges of other white spots or markings A roan horse may not fit into any of the traditional categories as there is much still to be learned about the genetics of roan. The existence of other types of roaning conditions not covered by those mentioned here is possible and likely. [2]
The genetics behind roan dogs are still unclear, and at present candidate genes have been ruled out. [6] There remains a great deal of ambiguity in terminology regarding mottled dogs, which are called roan, ticked, mottled and belton depending on the context. The roan or ticked color is described in many breeds of gundogs such as English Cocker Spaniels, American Cocker Spaniels, English Springer Spaniels, Field Spaniels and Brittanys, German Longhaired Pointers, German Shorthaired Pointers, Bracchi Italiani, Spinoni Italiani, Lagotti Romagnoli, English Setters, Small Münsterländer as well as Border Collies and many other breeds.
In dogs, roan manifests itself only in unpigmented areas, the presence and shape of which are determined by other genes. [7] This is in stark contrast to true roan horses and roan cattle, which are roan only in pigmented regions of their coat and may have white markings. Instead, dogs with roaning or ticking are born with clear, open white markings which begin to fill in with flecking in the subsequent weeks and continue to darken with age. [8] Most breed standards use the terms "ticked" and "roan" interchangeably, with the former referring to clearly defined flecks on a white background and the latter to flecks so closely spaced that the mixture appears even. [9]
The terminology that relates the underlying coat color with the roan modifier is often breed-specific, but most standards call a black dog with roaning blue. In breeds that are characterized by roaning and ticking such as the Large Munsterlander, clear white-marked individuals may be called plated. [7] The term belton is reserved for English Setters.
In 1957, Little suggested that roan and ticking were controlled separately, and postulated that roan may have been homologous to "silvered" coat in mice. [9] This condition in mice is actually homologous to merle, which might be described by some as "roan." [10] In 2007, the gene responsible for roan cattle (KITLG) was refuted as a possible cause of roan in dogs. Neither roan nor ticking, if they are independently caused, appear to be recessive. [6]
Breeds of cattle known for roans are the Belgian Blue and Shorthorn. Among the former, coat color may be solid black, solid white, or blue roan; the latter may be solid red, solid white, or red roan. Belgian Blues also typically exhibit spotting patterns, [11] which are genetically separate from roan. As a result, most roan cows exhibit blotches of clearly colored and clearly white hair, with roan patches. [12] Some "cryptic" roan cattle appear solid, but upon close inspection reveal a small roan patch. [13] Roan cattle cannot "breed true" but breeding white cattle to a solid mate will always yield a roan calf. The white color typical of Charolais and White Park breeds is not related to roan. [14]
Roan in Shorthorns and Belgian Blues is controlled by the mast cell growth factor (MGF) gene, also called the steel locus, on bovine chromosome 5. [15] Part of the KIT ligand, this region is involved in many cell differentiation processes. Mast cell growth factor promotes pigment production by pigment cells, [16] and without it, skin and hair cells lack pigment. With two functional MGF genes (homozygous dominant), cattle are fully pigmented; without any functional MGF genes (homozygous recessive), they are white. MGF-controlled roan occurs when cattle possess one functional and one non-functional MGF gene (heterozygous), resulting in a roughly even mixture of white regions and colored regions. [13]
The reproductive condition "White Heifer Disease," associated with the MGF gene, is characterized by homozygous MGF-white heifers with incomplete reproductive tracts. [17]
The roan coloration of guinea pigs is linked to microphthalmia. The allele that controls roaning in guinea pigs is incompletely dominant: an animal with one copy of the allele will have varying amounts of white hair scattered through its coat, particularly on the back and sides.
About 25% of guinea pigs born to two roans are completely white, having two copies of the "roan" allele, and may have a constellation of deformities associated with "lethal white syndrome", although this condition has no relation to overo lethal white syndrome in horses or double merle syndrome in dogs. Lethal white guinea pigs ("lethals") often die shortly after birth or at weaning age, but with hand-feeding and regular dental care, lethals may live 2 to 3 years. Some lethals have reportedly lived to 6 or 7 years. It is worth noting that, unlike anophthalmic hamsters, guinea pigs with the condition are not sterile, but females may be unable to deliver live young.
Lethal white syndrome symptoms include:
Roan coloration is not to be confused with the "magpie" coloration of guinea pigs, which is a brindle color lacking red pigment due to the "chinchilla" allele, an allele also responsible for self white and silver agouti coloration.
The American Paint Horse is a breed of horse that combines both the conformational characteristics of a western stock horse with a pinto spotting pattern of white and dark coat colors. Developed from a base of spotted horses with Quarter Horse and Thoroughbred bloodlines, the American Paint Horse Association (APHA) breed registry is now one of the largest in North America. The registry allows some non-spotted animals to be registered as "Solid Paint Bred" and considers the American Paint Horse to be a horse breed with distinct characteristics, not merely a color breed.
A dilution gene is any one of a number of genes that act to create a lighter coat color in living creatures. There are many examples of such genes:
A piebald or pied animal is one that has a pattern of unpigmented spots (white) on a pigmented background of hair, feathers or scales. Thus a piebald black and white dog is a black dog with white spots. The animal's skin under the white background is not pigmented.
Bay is a hair coat color of horses, characterized by a reddish-brown or brown body color with a black point coloration on the mane, tail, ear edges, and lower legs. Bay is one of the most common coat colors in many horse breeds.
Brindle is a coat coloring pattern in animals, particularly dogs, cattle, guinea pigs, cats, and, rarely, horses. It is sometimes described as "tiger-striped", although the brindle pattern is more subtle than that of a tiger's coat.
Point coloration is animal coat coloration with a pale body and relatively darker extremities, i.e. the face, ears, feet, tail, and scrotum. It is most recognized as the coloration of Siamese and related breeds of cat, but can be found in dogs, rabbits, rats, sheep, guinea pigs and horses as well.
A gray horse has a coat color characterized by progressive depigmentation of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike some equine dilution genes and some other genes that lead to depigmentation, gray does not affect skin or eye color. Gray horses may be born any base color, depending on other color genes present. White hairs begin to appear at or shortly after birth and become progressively more prevalent as the horse ages as white hairs become intermingled with hairs of other colors. Graying can occur at different rates—very quickly on one horse and very slowly on another. As adults, most gray horses eventually become completely white, though some retain intermixed light and dark hairs.
Equine coat color genetics determine a horse's coat color. Many colors are possible, but all variations are produced by changes in only a few genes. Bay is the most common color of horse, followed by black and chestnut. A change at the agouti locus is capable of turning bay to black, while a mutation at the extension locus can turn bay or black to chestnut.
Merle is a genetic pattern in a dog's coat and alleles of the PMEL gene. It results in different colors and patterns and can affect any coats. The allele creates mottled patches of color in a solid or piebald coat, blue or odd-colored eyes, and can affect skin pigment as well. Two types of colored patches generally appear in a merle coat: brown/liver and black. Associated breeds include Carea Leonés, Australian Shepherds and Catahoula Leopard Dogs. Health issues are more typical and more severe when two merle-patterned dogs are bred together.
Overo refers to several genetically unrelated pinto coloration patterns of white-over-dark body markings in horses, and is a term used by the American Paint Horse Association to classify a set of pinto patterns that are not tobiano. Overo is a Spanish word, originally meaning "like an egg". The most common usage refers to frame overo, but splashed white and sabino are also considered "overo". A horse with both tobiano and overo patterns is called tovero.
Horses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them.
A white horse is born predominantly white and stays white throughout its life. A white horse has mostly pink skin under its hair coat, and may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white (W) genes, are rare. Most horses that are commonly referred to as "white" are actually "gray" horses whose hair coats are completely white. Gray horses may be born of any color and their hairs gradually turn white as time goes by and take on a white appearance. Nearly all gray horses have dark skin, except under any white markings present at birth. Skin color is the most common method for an observer to distinguish between mature white and gray horses.
Black is a hair coat color of horses in which the entire hair coat is black. Black is a relatively uncommon coat color, and it is not uncommon to mistake dark chestnuts or bays for black.
Sabino describes a distinct pattern of white spotting in horses. In general, Sabino patterning is visually recognized by roaning or irregular edges of white markings, belly spots, white extending past the eyes or onto the chin, white above the knees or hocks, and "splash" or "lacy" marks anywhere on the body. Some sabinos have patches of roan patterning on part of the body, especially the barrel and flanks. Some sabinos may have a dark leg or two, but many have four white legs. Sabino patterns may range from slightly bold face or leg white markings—as little as white on the chin or lower lip—to horses that are fully white.
Rabicano, sometimes called white ticking, is a horse coat color characterized by limited roaning in a specific pattern: its most minimal form is expressed by white hairs at the top of a horse's tail, often is expressed by additional interspersed white hairs seen first at the flank, then other parts of the body radiating out from the flank, where the white hairs will be most pronounced. Rabicano is distinct from true roan, which causes evenly interspersed white hairs throughout the body, except for solid-colored head and legs.
The leopard complex is a group of genetically related coat patterns in horses. These patterns range from progressive increases in interspersed white hair similar to graying or roan to distinctive, Dalmatian-like leopard spots on a white coat. Secondary characteristics associated with the leopard complex include a white sclera around the eye, striped hooves and mottled skin. The leopard complex gene is also linked to abnormalities in the eyes and vision. These patterns are most closely identified with the Appaloosa and Knabstrupper breeds, though its presence in breeds from Asia to western Europe has indicated that it is due to a very ancient mutation.
Dominant white (W) is a group of genetically related coat color alleles on the KIT gene of the horse, best known for producing an all-white coat, but also able to produce various forms of white spotting, as well as bold white markings. Prior to the discovery of the W allelic series, many of these patterns were described by the term sabino, which is still used by some breed registries.
Roan is a horse coat color pattern characterized by an even mixture of colored and white hairs on the body, while the head and "points"—lower legs, mane, and tail—are mostly solid-colored. Horses with roan coats have white hairs evenly intermingled throughout any other color. The head, legs, mane, and tail have fewer scattered white hairs or none at all. The roan pattern is dominantly inherited, and is found in many horse breeds. While the specific mutation responsible for roan has not been exactly identified, a DNA test can determine zygosity for roan in several breeds. True roan is always present at birth, though it may be hard to see until after the foal coat sheds out. The coat may lighten or darken from winter to summer, but unlike the gray coat color, which also begins with intermixed white and colored hairs, roans do not become progressively lighter in color as they age. The silvering effect of mixed white and colored hairs can create coats that look bluish or pinkish.
Dogs have a wide range of coat colors, patterns, textures and lengths. Dog coat color is governed by how genes are passed from dogs to their puppies and how those genes are expressed in each dog. Dogs have about 19,000 genes in their genome but only a handful affect the physical variations in their coats. Most genes come in pairs, one being from the dog's mother and one being from its father. Genes of interest have more than one expression of an allele. Usually only one, or a small number of alleles exist for each gene. In any one gene locus a dog will either be homozygous where the gene is made of two identical alleles or heterozygous where the gene is made of two different alleles.
The agouti gene, the Agouti-signaling protein (ASIP) is responsible for variations in color in many species. Agouti works with extension to regulate the color of melanin which is produced in hairs. The agouti protein causes red to yellow pheomelanin to be produced, while the competing molecule α-MSH signals production of brown to black eumelanin. In wildtype mice, alternating cycles of agouti and α-MSH production cause agouti coloration. Each hair has bands of yellow which grew during agouti production, and black which grew during α-MSH production. Wildtype mice also have light-colored bellies. The hairs there are a creamy color the whole length because the agouti protein was produced the whole time the hairs were growing.
in Seitz et al. (1999)
in Seitz et al. (1999)
| Base coat colors |
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| Gray | |||||||||||
| Dilution genes |
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| White | |||||||||||
Horse markings and patterns |
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| Other | |||||||||||
| Genetics and breeding | |||||||||||