White (horse)

Last updated November 04, 2019

White horses are born white and stay white throughout their lives. White horses 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 and may be born of any color and gradually "gray" as time goes on and take on a white appearance.^[1]

Dominant white Horse coat color and its genetics

Dominant white or white spotting is a group of genetically related coat color conditions in the horse, best known for producing an all-white coat, but also able to produce various forms of white spotting and white markings, several of which are sometimes referred to as sabino.

Gray or grey is a coat color of horses characterized by progressive silvering of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike many depigmentation genes, gray does not affect skin or eye color. Their adult hair coat is white, dappled, or white intermingled with hairs of other colors. 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 lighter as the horse ages. Graying can occur at different rates—very quickly on one horse and very slowly on another.

True white horses

White horses have unpigmented skin and a white hair coat. Many white horses have dark eyes, though some have blue eyes. In contrast to gray horses which are born with pigmented skin they keep for life and pigmented hair that lightens to white with age, truly white horses are born with white hair and mostly pink, unpigmented skin. Some white horses are born with partial pigmentation in their skin and hair, which may or may not be retained as they mature, but when a white horse lightens, both skin and hair lose pigmentation. In contrast, grays retain skin pigment and only the hair becomes white.

White colorings, whether white markings, white patterns or dominant white are collectively known as depigmentation phenotypes, and are all caused by areas of skin that lack pigment cells (melanocytes).^[2] Depigmentation phenotypes have various genetic causes, and those that have been studied usually map to the EDNRB and KIT genes. However, much about the genetics behind various all-white depigmentation phenotypes are still unknown.

Markings on horses are usually distinctive white areas on an otherwise dark base coat color. Most horses have some markings, and they help to identify the horse as a unique individual. Markings are present at birth and do not change over the course of the horse's life. Most markings have pink skin underneath most of the white hairs, though a few faint markings may occasionally have white hair with no underlying pink skin. Markings may appear to change slightly when a horse grows or sheds its winter coat, however this difference is simply a factor of hair coat length; the underlying pattern does not change.

A pinto horse has a coat color that consists of large patches of white and any other color. The distinction between "pinto" and "solid" can be tenuous, as so-called "solid" horses frequently have areas of white hair. Various cultures throughout history appear to have selectively bred for pinto patterns.

In genetics, the phenotype of an organism is the composite of the organism's observable characteristics or traits. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological properties, its behavior, and the products of behavior. An organism's phenotype results from two basic factors: the expression of an organism's genetic code, or its genotype, and the influence of environmental factors. Both factors may interact, further affecting phenotype. When two or more clearly different phenotypes exist in the same population of a species, the species is called polymorphic. A well-documented example of polymorphism is Labrador Retriever coloring; while the coat color depends on many genes, it is clearly seen in the environment as yellow, black, and brown. Richard Dawkins in 1978 and then again in his 1982 book The Extended Phenotype suggested that one can regard bird nests and other built structures such as caddis-fly larvae cases and beaver dams as "extended phenotypes".

Dominant white

Dominant white is best known for producing pink-skinned all-white horses with brown eyes, though some dominant white horses have residual pigment along the topline. Dominant white has been studied in Thoroughbreds, Arabian horses, the American White horse, the Camarillo White horse, and several other breeds. There are 27 identified variants of dominant white as of 2017, plus sabino 1, each corresponding to a spontaneously-white foundation animal and a mutation on the KIT gene. Researchers have suggested that at least some forms of dominant white result in nonviable embryos in the homozygous state, though others are known to be viable as homozygotes. While homologous mutations in mice are often linked to anemia and sterility, no such effects have been observed in dominant white horses. Dominant white horses typically have white noses that can be subject to sunburn.

The Thoroughbred is a horse breed best known for its use in horse racing. Although the word thoroughbred is sometimes used to refer to any breed of purebred horse, it technically refers only to the Thoroughbred breed. Thoroughbreds are considered "hot-blooded" horses that are known for their agility, speed, and spirit.

Arabian horse Horse breed originating in the Middle East

The Arabian or Arab horse is a breed of horse that originated on the Arabian Peninsula. With a distinctive head shape and high tail carriage, the Arabian is one of the most easily recognizable horse breeds in the world. It is also one of the oldest breeds, with archaeological evidence of horses in the Middle East that resemble modern Arabians dating back 4,500 years. Throughout history, Arabian horses have spread around the world by both war and trade, used to improve other breeds by adding speed, refinement, endurance, and strong bone. Today, Arabian bloodlines are found in almost every modern breed of riding horse.

Camarillo White Horse American horse breed

The Camarillo White Horse is a rare horse breed less than 100 years old known for its pure white color. It dates back to 1921, when Adolfo Camarillo, one of the last Californios, purchased a 9-year-old stallion named Sultan at the California State Fair in Sacramento. The California White horse was owned and bred by the Camarillo family until the death of Adolfo Camarillo’s daughter Carmen in 1987.

Sabino-white

Sabino-white horses are pink-skinned with all-white or nearly-white coats and dark eyes. They are homozygous for the dominant SB1 allele at the Sabino 1 locus, which has been mapped to KIT .^[5] Without a DNA test, Sabino-white horses are indistinguishable from dominant white horses. The Sabino1 allele, and the associated spotting pattern, is found in Miniature horses, American Quarter Horses, American Paint Horses, Tennessee Walkers, Missouri Fox Trotters, Mustangs, Shetland Ponies, and Aztecas.^[6] Sabino 1 has not been found in the Arabian horse, Clydesdale,^[5] Thoroughbred, Standardbred horse, or Shire horse. The Sabino 1 allele is not linked to any health defects, though sabino-whites may need some protection from sunburn. Horses with only one copy of the Sabino1 gene usually have dramatic spotting, including two or more white legs, often with white running up the front of the leg, extensive white on the face, spotting on the midsection, and jagged or roaned margins to the pattern.^[5]

An allele is a variant form of a given gene. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation. A notable example of this trait of color variation is Gregor Mendel's discovery that the white and purple flower colors in pea plants were the result of "pure line" traits which could be used as a control for future experiments. However, most alleles result in little or no observable phenotypic variation.

Locus (genetics) location of a gene at a chromosome

In genetics, a locus is a specific, fixed position on a chromosome where a particular gene or genetic marker is located. Each chromosome carries many genes, with each gene occupying a different position or locus; in humans, the total number of protein-coding genes in a complete haploid set of 23 chromosomes is estimated at 19,000–20,000.

Mast/stem cell growth factor receptor (SCFR), also known as proto-oncogene c-KIT or tyrosine-protein kinase KIT or CD117, is a receptor tyrosine kinase protein that in humans is encoded by the KIT gene. Multiple transcript variants encoding different isoforms have been found for this gene. KIT was first described by the German biochemist Axel Ullrich in 1987 as the cellular homolog of the feline sarcoma viral oncogene v-kit.

This "white-born" or "fewspot" Appaloosa foal has a mostly pink-skinned white coat. WeissgeborenerAppaloosa.jpg — This "white-born" or "fewspot" Appaloosa foal has a mostly pink-skinned white coat.

White born leopards

The leopard complex, related to the Leopard (LP) gene, characterizes the Appaloosa and Knabstrupper breeds with their spotted coats. Leopard is genetically quite distinct from all other white and white-spotting patterns. The fewspot leopard pattern, however, can resemble white. Two factors influence the eventual appearance of a leopard complex coat: whether one copy (heterozygous LP/lp) or two copies (homozygous LP/LP) Leopard alleles are present, and the degree of dense white patterning present at birth.^[7] If a foal is homozygous for the LP allele and has extensive dense white patterning, they will appear nearly white at birth, and may continue to lighten with age. In other parts of the world, these horses are called "white born."^[8] "White born" foals are less common among Appaloosa horses than Knabstruppers or Norikers, as the extensive dense white patterning is favored for producing dramatic full leopards. Homozygous leopards have the LP/LP genotype, and may be varnish roan, fewspot leopard, or snowcap patterned. Homozygous leopards are substantially more prone to congenital stationary night blindness.^[9] Congenital stationary night blindness is present at birth and is characterized by impaired vision in dark conditions.

The Appaloosa is an American horse breed best known for its colorful spotted coat pattern. There is a wide range of body types within the breed, stemming from the influence of multiple breeds of horses throughout its history. Each horse's color pattern is genetically the result of various spotting patterns overlaid on top of one of several recognized base coat colors. The color pattern of the Appaloosa is of interest to those who study equine coat color genetics, as it and several other physical characteristics are linked to the leopard complex mutation (LP). Appaloosas are prone to develop equine recurrent uveitis and congenital stationary night blindness; the latter has been linked to the leopard complex.

The Knabstrupper, also called Knabstrup horse, is a Danish breed of horse with an unusual range of coat coloration.

Varnish roan describes a horse with coloration similar to roan, but with some changes in color over the years, though not to the extreme of a gray. This type of roaning only occurs in conjunction with the Leopard complex. Varnish roans are born with a dark base coat color, usually with some spotting. As the horse ages, white hairs increase over most of the body, and many spotted markings blur or fade. The varnish roan pattern often appears to spread from the white of any original markings. This color pattern is best known in the Appaloosa breed of horse.

Lethal white syndrome

Lethal white syndrome is a genetic disorder linked to the Frame overo (O) gene and most closely studied in the American Paint Horse. Affected foals are carried to term and at birth appear normal, though they have pink-skinned all-white or nearly-white coats and blue eyes. However, the colon of these foals cannot function due to the absence of nerve cells, and the condition cannot be treated. Foals with Lethal White Syndrome invariably die of colic within 72 hours, and are usually humanely euthanized. Carriers of the gene, who are healthy and normal, can be identified by a DNA test. While carriers often exhibit the "frame overo" pattern, this is not a dispositive trait and testing is necessary, as the pattern can appear in a minimal form as normal white markings or be masked by other white spotting genes.

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".There are at least three genetically different spotting patterns which fall under the "overo" classification: frame overo, sabino overo, and splash or splashed white overo.

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.

Foal A horse of either sex up to the age of one year

A foal is an equine up to one year old; this term is used mainly for horses. More specific terms are colt for a male foal and filly for a female foal, and are used until the horse is three or four. When the foal is nursing from its great (mother), it may also be called a "suckling". After it has been weaned from its dam, it may be called a "weanling". When a mare is pregnant, she is said to be "in foal". When the mare gives birth, she is "foaling", and the impending birth is usually stated as "to foal". A newborn horse is "foaled".

Horses that appear white, but are not

True white horses have unpigmented pink skin and unpigmented white hair, though eye color varies. The lack of pigment in the skin and hair is caused by the absence of pigment-producing cells called melanocytes. Some coat colors are characterized by light or white-like coats and even pinkish skin, however these white-like coats are not lacking melanocytes. Instead, white-like coat colors result from various changes in the ways melanocytes produce pigment.

Gray

Gray horses have the most common "white-like" coat color. However, the most noticeable difference between a gray horse whose hair coat is completely white and a white horse is skin color: most gray horses have black skin and dark eyes, white horses have light, unpigmented skin. The gray gene does not affect skin or eye color, so grays typically have dark skin and eyes, as opposed to the unpigmented pink skin of true white horses.^[10] The skin and eyes may be other colors if influenced by other factors such as white markings, certain white spotting patterns or dilution genes. Gray foals may be born any color, but the colored hairs of their coat become progressively silvered as they age, eventually giving mature gray horses a white or nearly-white hair coat. Gray is controlled by a single dominant allele of a gene that regulates specific kinds of stem cells.^[11] Gray horses are at an increased risk for melanoma; 70-80% of gray horses over the age of 15 have a melanoma tumor.^[11]

This "Ivory Champagne" foal has both cream dilution and champagne dilution genes, shown by DNA testing as well as visibly semi-pigmented, rosy skin and a cream-colored coat that can be mistaken for white. This same hair coat shade would be considered cremello if the horse had double cream dilution, but still would not be white. Ivory Champange.jpg — This "Ivory Champagne" foal has both cream dilution and champagne dilution genes, shown by DNA testing as well as visibly semi-pigmented, rosy skin and a cream-colored coat that can be mistaken for white. This same hair coat shade would be considered cremello if the horse had double cream dilution, but still would not be white.

Diluted coat colors

True white hair is rooted in unpigmented skin that lacks melanocytes. In contrast, diluted coat colors have melanocytes, but vary due to the concentration or chemical structure of the pigments made by these pigment-producing cells, not the absence of the cells themselves. There are at least five known types of pigment dilution in horses, three which, as described below, can act to produce off-white phenotypes. Horses with strongly diluted coat colors usually have pale blue eyes, cream-colored coats, and rosy-pink skin. White markings are usually visible upon closer inspection.

The Cream gene produces two types of diluted color. Cremellos, perlinos, and smoky creams have rosy-pink skin, pale blue eyes, and cream-colored coats that can appear almost white. These coat colors, collectively called "double dilutes" or "blue-eyed creams", result when a horse is homozygous for the cream gene. When heterozygous, the cream gene is also responsible for palomino and buckskin. A few Palominos have a very light hair coat is occasionally mistaken for either cremello or white. White markings and patterns are visible against the slightly-pigmented coat and skin. The cream gene is not known to be associated with any health problems.
Pearl-Cream pseudo-double dilute occurs when a horse has one cream gene and one pearl gene. These two distinct dilution factors interact to produce a cremello-like coat. Pearl-creams have pale but pigmented skin and blue-green eyes, and are distinctly pale cream-colored.^[12] To date, the Pearl gene has been found in Quarter Horses, Paint horses, and some Iberian horses.^[13] Pearl is not known to be associated with any health problems.
Champagne-Cream pseudo-double dilute occurs when a horse has one cream gene and one champagne gene. Champagne and cream are another pair of unrelated dilution factors that interact to produce a cremello-like coat. Champagne-creams have freckled, pinkish skin, pale eyes, and pale coats. These colors were formerly referred to as "ivory champagnes".^[14] Champagne is found in North American breeds such as the American Cream Draft, Tennessee Walking Horse, American Saddlebred, American Quarter Horse, and Miniature horse. It is not known to be associated with any health problems.

Albinism

Although white horses are sometimes called "albino" there are no reported cases of a true "albino" horse.^[15] There are also references in literature calling white horses "albino".^[16] Dominant white in horses is caused by the absence of pigment cells (melanocytes), whereas albino animals have a normal distribution of melanocytes.^[17] In other animals, patches of unpigmented skin, hair, or eyes due to the lack of pigment cells (melanocytes) are called piebaldism, not albinism nor partial albinism.

All so-called "albino" horses have pigmented eyes, generally brown or blue. In contrast, many albino mammals, such as mice or rabbits, typically have a white hair coat, unpigmented skin and reddish eyes. The definition of "albinism" varies depending on whether humans, other mammals, or other vertebrates are being discussed.^[18]

Despite this, some registries still refer to "albino" horses. For example, the Paso Fino Horse Association registers cremellos and other cream colors as "albino."^[19] Until 1999, the American Quarter Horse Association (AQHA) described perlino or cremello horses as "albino" in rule 227(j).^[20] The AQHA later replaced the word "albino" with "cremello or perlino," and in 2002 the rule was removed entirely. Among Connemara pony breeders, homozygous creams are called "blue-eyed creams" or sometimes "pseudo-albino".^[21]

Types of albinism in humans and other animals

The best-known type of albinism is OCA1A, which impairs tyrosinase production. In other mammals, the diagnosis of albinism is based on the impairment of tyrosinase production through defects in the Color (C) gene.^[22] Mice and other mammals without tyrosinase have unpigmented pink skin, unpigmented white hair, unpigmented reddish eyes, and some form of vision impairment. No mutations of the tyrosinase or C gene are known in horses.^[15]

Humans exhibit a wide range of pigmentation levels as a species. However, the diagnosis of albinism in humans is based on visual impairment, which has not been described in white horses.^[23] Vision problems are not associated with gray, dilute, or white coat colors in horses, and blue eyes in horses do not indicate poor vision. Eyes are pigmented at the front of the iris called the stroma, and in a thin layer at the back of the iris in tissue called the iris pigment epithelium. The iris pigment epithelium prevents damaging light scattering within the eye. Blue-eyed humans and mammals have little or no pigment in the stroma, but retain pigment in the iris pigment epithelium. If pigment is missing from both the stroma and the iris pigment epithelium, the only pigment in the eye is the hemoglobin in blood vessels. This accounts for the reddish appearance of eyes in some types of albinism.^[24]

In research mammals, such as mice, albinism is more strictly defined. Albino mice occur due to a recessive mutation of the C gene. No such mutation exists in horses.^[15] Albino mice lack pigment, but "...the inability of albino animals to produce pigment stems not from an absence of melanocytes...but from a deficiency and/or alteration of the structure of tyrosinase in melanocytes which are otherwise normal."^[17] This definition of albinism in mice - the inability to make tyrosinase - is extended to other mammals.^[22]

While mammals derive their pigments only from melanins, fish, reptiles and birds rely on a number of pigments apart from melanins: carotenoids, porphyrins, psittacofulvins, pterins, etc.^[18]^[25] Most commonly, reptiles with a condition homologous to human OCA1A retain their reddish and orangish hues. As a result, birds and reptiles without the ability to manufacture tyrosinase are more accurately described as "amelanistic." Horses do not have non-melanin pigments and so if they were albino, would have no pigmentation. The retained pigment of dilute horses, like cremellos, is not comparable to the retained pigment of amelanistic "albino" birds and reptiles.

Why cream is not albino

The cream gene, which is responsible for palomino, buckskin, and cremello coat colors, was mapped to the MATP gene in 2003.^[26] This gene is sometimes called the OCA4 gene, because one mutation on MATP is associated with oculocutaneous albinism type 4. However, other benign mutations on MATP are responsible for normal variations in skin, hair, and eye color in humans.^[27]MATP is not the "albino gene"; one of many mutations of the human MATP is responsible for a form of albinism.

Famous white horses

Many famous horses, past and present, were alleged to be "white" by observers, but were actually grays with hair coats turned fully white. Likewise, most white horses used in movies are actually grays, in part because they are easier to find.

However, there are a few truly white horses who were used in film. One of the best-known examples was "Silver," ridden by the Lone Ranger, a role actually played by two different white horses. At least one horse who played "Topper," ridden by Hopalong Cassidy, was also white. Another famous white horse is Yukichan , a Japanese Thoroughbred racehorse who won the Kanto Oaks at Kawasaki Racecourse.^[28]

Mythology

Throughout history, white horses have been mythologized in many cultures. For example, Herodotus reported that white horses were held as sacred animals in the Achaemenid court of Xerxes the Great (ruled 486-465 BC),^[29] In more than one tradition, a white horse carries patron saints or the world saviour in the end times, including Hinduism, Christianity, and Islam. ^{[ citation needed ]}

Related Research Articles

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:

Lethal white syndrome (LWS), also called overo lethal white syndrome (OLWS), lethal white overo (LWO), and overo lethal white foal syndrome (OLWFS), is an autosomal genetic disorder most prevalent in the American Paint Horse. Affected foals are born after the full 11-month gestation and externally appear normal, though they have all-white or nearly all-white coats and blue eyes. However, internally, these foals have a nonfunctioning colon. Within a few hours, signs of colic appear; affected foals die within a few days. Because the death is often painful, such foals are often humanely euthanized once identified. The disease is particularly devastating because foals are born seemingly healthy after being carried to full term.

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 brown body color with a black mane, tail, ear edges, and lower legs. Bay is one of the most common coat colors in many horse breeds.

Cream gene gene responsible for a number of horse coat colors

The cream gene is responsible for a number of horse coat colors. Horses that have the cream gene in addition to a base coat color that is chestnut will become palomino if they are heterozygous, having one copy of the cream gene, or cremello, if they are homozygous. Similarly, horses with a bay base coat and the cream gene will be buckskin or perlino. A black base coat with the cream gene becomes the not-always-recognized smoky black or a smoky cream. Cream horses, even those with blue eyes, are not white horses. Dilution coloring is also not related to any of the white spotting patterns.

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.

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. Extension and agouti are particularly well-known genes with dramatic effects. Differences at the agouti gene determine whether a horse is bay or black, and a change to the extension gene can make a horse chestnut instead. Most domestic horses have a variant of the dun gene which saturates the coat with color so that they are bay, black, or chestnut instead of dun, grullo, or red dun. A mutation called cream is responsible for palomino, buckskin, and cremello horses. Pearl, champagne and silver dapple also lighten the coat, and sometimes the skin and eyes as well. Genes that affect the distribution of melanocytes create patterns of white such as in roan, pinto, leopard, white, and even white markings. Finally, the gray gene causes premature graying, slowly adding white hairs over the course of several years until the horse looks white. Some of these patterns have complex interactions.

Chestnut is a hair coat color of horses consisting of a reddish-to-brown coat with a mane and tail the same or lighter in color than the coat. Chestnut is characterized by the absolute absence of true black hairs. It is one of the most common horse coat colors, seen in almost every breed of horse.

Equine coat color Horse coat colors and markings

Horses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them.

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 is a group of white spotting patterns in horses that affect the skin and hair. A wide variety of irregular color patterns are accepted as sabino. In the strictest sense, "sabino" refers to the white patterns produced by the Sabino 1 (SB1) gene, for which there is a DNA test. However, other horse enthusiasts also refer to patterns that are visually similar to SB1 as "sabino", even if testing indicates the gene is not present. Use of the term to describe non-SB1 "sabino" patterns in breeds that apparently do not carry the gene is hotly debated by both researchers and horse breeders.

Smoky black is a hair coat color of horses in which the coat is either black or a few shades lighter than true black. Smoky black is produced by the action of a heterozygous cream gene on an underlying black coat color. Therefore, smoky black is a member of the cream family of coat color dilutions, and found in horse populations that have other cream gene-based colors such as palomino, buckskin, perlino and cremello. All smoky blacks must have at least one parent with the cream gene, and a smoky black can be verified through DNA testing. Smoky black has been mistaken for faded black, dark bay or brown, grullo or even liver chestnut.

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 it is due to a very ancient mutation and used to be widespread.

Amelanism is a pigmentation abnormality characterized by the lack of pigments called melanins, commonly associated with a genetic loss of tyrosinase function. Amelanism can affect fish, amphibians, reptiles, birds, and mammals including humans. The appearance of an amelanistic animal depends on the remaining non-melanin pigments. The opposite of amelanism is melanism, a higher percentage of melanin.

Seal brown is a hair coat color of horses characterized by a near-black body color; with black points, the mane, tail and legs; but also reddish or tan areas around the eyes, muzzle, behind the elbow and in front of the stifle. The term is not to be confused with "brown", which is used by some breed registries to refer to either a seal brown horse or to a dark bay without the additional characteristics of seal brown genetics.

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.

In poultry standards, solid white is coloration of plumage in chickens characterized by a uniform pure white color across all feathers, which is not generally associated with depigmentation in any other part of the body.

References

↑ "Introduction to Coat Color Genetics" from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008
↑ Rieder, Stefan; Christian Hagger; Gabriela Obexer-Ruff; Tosso Leeb; Pierre-André Poncet (2008-02-21). "Genetic Analysis of White Facial and Leg Markings in the Swiss Franches-Montagnes Horse Breed". Journal of Heredity. The American Genetic Association. 99 (2): 130–6. doi:10.1093/jhered/esm115. PMID 18296388 . Retrieved 2009-07-03. Phenotypes may vary from tiny depigmentated body spots to white head and leg markings, further on to large white spotting and finally nearly complete depigmentation in white-born horses...White markings result from the lack of melanocytes in the hair follicles and the skin...A completely pigmented head or leg depends on the complete migration and clonal proliferation of the melanoblasts in the mesoderm of the developing fetus, thus ensuring that limbs and the head acquire a full complement of melanocytes
↑ Kathman, Lesli(2014). "The Equine Tapestry", p. 83, 90-94. Blackberry Lane Press.
↑ "YUCHICHAN".
1 2 3 UC Davis. "Horse Coat Color Tests". Veterinary Genetics Laboratory. University of California - Davis. Retrieved 2009-07-08. Horses with 2 copies of the Sabino1 gene, are at least 90% white and are referred to as Sabino-white.
↑ Brooks, Samantha (2005). "The SNP was found among American Miniature Horses, American Paint Horses, Azteca, Missouri Fox Trotters, Shetland Ponies, and Spanish Mustangs."
↑ Sheila Archer (2008-08-31). "Studies Currently Underway". The Appaloosa Project. Retrieved 2008-11-04.
↑ "Die Farbmerkmale" (in German). Knabstrupper.de. Retrieved 2009-06-20.
↑ Sandmeyer, Lynne S.; Carrie B. Breaux; Sheila Archer; Bruce H. Grahn (2007). "CSNB and Leopard Complex in Appaloosas". 10 (6). American College of Veterinary Ophthalmologists: 368–375. doi:10.1111/j.1463-5224.2007.00572.x. PMID 17970998.Cite journal requires |journal= (help)
↑ Locke, MM; MCT Penedo; SJ Bricker; LV Millon; JD Murray (2002). "Linkage of the grey coat colour locus to microsatellites on horse chromosome 25". Animal Genetics. International Society for Animal Genetics. 33 (5): 329–337. doi:10.1046/j.1365-2052.2002.00885.x. PMID 12354140. The progressive loss of colour in the hair of grey horses is controlled by a dominantly inherited allele at the Grey locus (GG). Foals are born any colour depending on the alleles present at other colour determining loci. After birth, horses carrying the GG allele begin to show white hairs that are intermixed with their original hair colour. Although the rate at which horses will turn grey is variable, the amount of white hair increases with age until the coat is completely white at maturity. Pigmentation of the skin and eyes is not affected by GG. Dark skin distinguishes the grey phenotype from that of pink-skinned cremello and white horses.
1 2 Pielberg, Gerli Rosengren; Anna Golovko; Elisabeth Sundström; Ino Curik; Johan Lennartsson; Monika H Seltenhammer; Thomas Druml; Matthew Binns; Carolyn Fitzsimmons; Gabriella Lindgren; Kaj Sandberg; Roswitha Baumung; Monika Vetterlein; Sara Strömberg; Manfred Grabherr; Claire Wade; Kerstin Lindblad-Toh; Fredrik Pontén; Carl-Henrik Heldin; Johann Sölkner; Leif Andersson (2008). "A cis-acting regulatory mutation causes premature hair graying and susceptibility to melanoma in the horse". Nature Genetics. 40 (8): 1004–1009. doi:10.1038/ng.185. PMID 18641652.
↑ UC Davis. "Horse Coat Color Tests". Veterinary Genetics Laboratory. University of California - Davis. Retrieved 2008-01-11. Pearl is known to interact with Cream dilution to produce pseudo-double Cream dilute phenotypes including pale skin and blue/green eyes.
↑ Stamatelakys, Irene (May 2009). "Precious Pearls" (PDF). Paint Horse Journal.
↑ "Champagne-Cream Combinations". International Champagne Horse Registry. Retrieved 2009-06-04.
1 2 3 Castle, William E (1948). "The ABC of Color Inheritance in Horses". Genetics. 33 (1): 22–35. PMC 1209395 . PMID 17247268. No true albino mutation of the color gene is known among horses, though several varieties of white horse are popularly known as albinos.
↑ O'Hara, Mary (1941). My Friend Flicka. Lippincott.
1 2 Silvers, Willys K. (1979). "3: The b-Locus and c (Albino) Series of Alleles". [http://www.informatics.jax.org/wksilvers/ The Coat Colors of Mice: A Model for Mammalian Gene Action and Interaction]. Springer Verlag. p. 59. Retrieved 2009-07-07. ...the inability of albino animals to produce pigment stems not from an absence of melanocytesExternal link in |title= (help)
1 2 Davis, Jeff (September–October 2007). "Color Abnormalities in Birds: A Proposed Nomenclature". Birding. American Birding Association. 39 (5).
↑ "Registration Application" (PDF). Paso Fino Horse Association. Retrieved 2009-07-04.
↑ "No horse is eligible for registration which possesses all three characteristics which designate a horse commonly known as an albino: light (or pink) skin over the body; white or cream colored hair over the body; and eyes of a bluish cast."
↑ Jeanette Gower (December 2002). "The Blue Eyed Cream Pony: Flawed or Value?" (PDF). Connemara Pony Breeders Society of Australia.
1 2 Cheville, Norman F (August 2006). Introduction to veterinary pathology (3 ed.). Wiley-Blackwell. ISBN 978-0-8138-2495-6. Albinism results from a structural gene mutation at the locus that codes for tyrosinase; that is, albino animals have a genetically determined failure of tyrosine synthesis.
↑ "What is Albinism?". The National Organization for Albinism and Hypopigmentation. Archived from the original on 2012-05-14. Retrieved 2009-07-07.
↑ Hamilton, Peter; Richard Gregson; Gary Edd Fish (1997). Text Atlas of the Retina (1 ed.). Informa Health Care. p. 151. ISBN 1-85317-226-X. In the most severe form, the latter may look pink since the only pigment present is hemoglobin within the iris blood vessels
↑ "Chromatophores". Learning Center. VMS. Retrieved 2009-07-07.
↑ Mariat, Denis; Sead Taourit; Gérard Guérin (2003). "A mutation in the MATP gene causes the cream coat colour in the horse". Genet. Sel. Evol. INRA, EDP Sciences. 35 (1): 119–133. doi:10.1051/gse:2002039. PMC 2732686 . PMID 12605854.
↑ Graf, J; Voisey J; Hughes I; van Daal A (July 2007). "Promoter polymorphisms in the MATP (SLC45A2) gene are associated with normal human skin color variation". Human Mutation. Wiley-Liss. 28 (7): 710–7. doi:10.1002/humu.20504. PMID 17358008.
↑ Yukichan horse pedigreequery
↑ "White Horses and Genetics". Archaeology.about.com. Retrieved 2010-04-29.

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.

[1] "Introduction to Coat Color Genetics" from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008

[rieder2008-2] Rieder, Stefan; Christian Hagger; Gabriela Obexer-Ruff; Tosso Leeb; Pierre-André Poncet (2008-02-21). "Genetic Analysis of White Facial and Leg Markings in the Swiss Franches-Montagnes Horse Breed". Journal of Heredity. The American Genetic Association. 99 (2): 130–6. doi:10.1093/jhered/esm115. PMID 18296388 . Retrieved 2009-07-03. Phenotypes may vary from tiny depigmentated body spots to white head and leg markings, further on to large white spotting and finally nearly complete depigmentation in white-born horses...White markings result from the lack of melanocytes in the hair follicles and the skin...A completely pigmented head or leg depends on the complete migration and clonal proliferation of the melanoblasts in the mesoderm of the developing fetus, thus ensuring that limbs and the head acquire a full complement of melanocytes

[EquineTapestry-3] Kathman, Lesli(2014). "The Equine Tapestry", p. 83, 90-94. Blackberry Lane Press.

[4] "YUCHICHAN".

[VGL-5] 1 2 3 UC Davis. "Horse Coat Color Tests". Veterinary Genetics Laboratory. University of California - Davis. Retrieved 2009-07-08. Horses with 2 copies of the Sabino1 gene, are at least 90% white and are referred to as Sabino-white.

[brooks2005-2-6] Brooks, Samantha (2005). "The SNP was found among American Miniature Horses, American Paint Horses, Azteca, Missouri Fox Trotters, Shetland Ponies, and Spanish Mustangs."

[archer-7] Sheila Archer (2008-08-31). "Studies Currently Underway". The Appaloosa Project. Retrieved 2008-11-04.

[DEKNN-8] "Die Farbmerkmale" (in German). Knabstrupper.de. Retrieved 2009-06-20.

[csnb-9] Sandmeyer, Lynne S.; Carrie B. Breaux; Sheila Archer; Bruce H. Grahn (2007). "CSNB and Leopard Complex in Appaloosas". 10 (6). American College of Veterinary Ophthalmologists: 368–375. doi:10.1111/j.1463-5224.2007.00572.x. PMID 17970998.Cite journal requires |journal= (help)

[locke2002-10] Locke, MM; MCT Penedo; SJ Bricker; LV Millon; JD Murray (2002). "Linkage of the grey coat colour locus to microsatellites on horse chromosome 25". Animal Genetics. International Society for Animal Genetics. 33 (5): 329–337. doi:10.1046/j.1365-2052.2002.00885.x. PMID 12354140. The progressive loss of colour in the hair of grey horses is controlled by a dominantly inherited allele at the Grey locus (GG). Foals are born any colour depending on the alleles present at other colour determining loci. After birth, horses carrying the GG allele begin to show white hairs that are intermixed with their original hair colour. Although the rate at which horses will turn grey is variable, the amount of white hair increases with age until the coat is completely white at maturity. Pigmentation of the skin and eyes is not affected by GG. Dark skin distinguishes the grey phenotype from that of pink-skinned cremello and white horses.

[pielberg-2008-11] 1 2 Pielberg, Gerli Rosengren; Anna Golovko; Elisabeth Sundström; Ino Curik; Johan Lennartsson; Monika H Seltenhammer; Thomas Druml; Matthew Binns; Carolyn Fitzsimmons; Gabriella Lindgren; Kaj Sandberg; Roswitha Baumung; Monika Vetterlein; Sara Strömberg; Manfred Grabherr; Claire Wade; Kerstin Lindblad-Toh; Fredrik Pontén; Carl-Henrik Heldin; Johann Sölkner; Leif Andersson (2008). "A cis-acting regulatory mutation causes premature hair graying and susceptibility to melanoma in the horse". Nature Genetics. 40 (8): 1004–1009. doi:10.1038/ng.185. PMID 18641652.

[davis-pearl-12] UC Davis. "Horse Coat Color Tests". Veterinary Genetics Laboratory. University of California - Davis. Retrieved 2008-01-11. Pearl is known to interact with Cream dilution to produce pseudo-double Cream dilute phenotypes including pale skin and blue/green eyes.

[stamatelakys-pearl-13] Stamatelakys, Irene (May 2009). "Precious Pearls" (PDF). Paint Horse Journal.

[ichrcream-14] "Champagne-Cream Combinations". International Champagne Horse Registry. Retrieved 2009-06-04.

[castle-15] 1 2 3 Castle, William E (1948). "The ABC of Color Inheritance in Horses". Genetics. 33 (1): 22–35. PMC 1209395 . PMID 17247268. No true albino mutation of the color gene is known among horses, though several varieties of white horse are popularly known as albinos.

[flicka-16] O'Hara, Mary (1941). My Friend Flicka. Lippincott.

[silvers1979-17] 1 2 Silvers, Willys K. (1979). "3: The b-Locus and c (Albino) Series of Alleles". [http://www.informatics.jax.org/wksilvers/ The Coat Colors of Mice: A Model for Mammalian Gene Action and Interaction]. Springer Verlag. p. 59. Retrieved 2009-07-07. ...the inability of albino animals to produce pigment stems not from an absence of melanocytesExternal link in |title= (help)

[birding-18] 1 2 Davis, Jeff (September–October 2007). "Color Abnormalities in Birds: A Proposed Nomenclature". Birding. American Birding Association. 39 (5).

[pfhaform-19] "Registration Application" (PDF). Paso Fino Horse Association. Retrieved 2009-07-04.

[aqha-20] "No horse is eligible for registration which possesses all three characteristics which designate a horse commonly known as an albino: light (or pink) skin over the body; white or cream colored hair over the body; and eyes of a bluish cast."

[gower-21] Jeanette Gower (December 2002). "The Blue Eyed Cream Pony: Flawed or Value?" (PDF). Connemara Pony Breeders Society of Australia.

[cheville-22] 1 2 Cheville, Norman F (August 2006). Introduction to veterinary pathology (3 ed.). Wiley-Blackwell. ISBN 978-0-8138-2495-6. Albinism results from a structural gene mutation at the locus that codes for tyrosinase; that is, albino animals have a genetically determined failure of tyrosine synthesis.

[NOAH-23] "What is Albinism?". The National Organization for Albinism and Hypopigmentation. Archived from the original on 2012-05-14. Retrieved 2009-07-07.

[retina-24] Hamilton, Peter; Richard Gregson; Gary Edd Fish (1997). Text Atlas of the Retina (1 ed.). Informa Health Care. p. 151. ISBN 1-85317-226-X. In the most severe form, the latter may look pink since the only pigment present is hemoglobin within the iris blood vessels

[VMS-25] "Chromatophores". Learning Center. VMS. Retrieved 2009-07-07.

[mariat2003-26] Mariat, Denis; Sead Taourit; Gérard Guérin (2003). "A mutation in the MATP gene causes the cream coat colour in the horse". Genet. Sel. Evol. INRA, EDP Sciences. 35 (1): 119–133. doi:10.1051/gse:2002039. PMC 2732686 . PMID 12605854.

[graf-27] Graf, J; Voisey J; Hughes I; van Daal A (July 2007). "Promoter polymorphisms in the MATP (SLC45A2) gene are associated with normal human skin color variation". Human Mutation. Wiley-Liss. 28 (7): 710–7. doi:10.1002/humu.20504. PMID 17358008.

[28] Yukichan horse pedigreequery

[29] "White Horses and Genetics". Archaeology.about.com. Retrieved 2010-04-29.