Roan (horse)
Encyclopedia
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
Mane (horse)
The mane is the hair that grows from the top of the neck of a horse or other equine, reaching from the poll to the withers, and includes the forelock or foretop. It is thicker and coarser than the rest of the horse's coat, and naturally grows to roughly cover the neck...

 and tail—are more solid-colored. The roan pattern is dominantly-inherited, and is found in many horse breed
Horse breed
Horse breed is a broad term with no clear consensus as to definition, but most commonly refers to selectively bred populations of domesticated horses, often with pedigrees recorded in a breed registry. However, the term is sometimes used in a very broad sense to define landrace animals, or...

s. While the specific mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

 responsible for roan has not been exactly identified, a DNA test can determine zygosity
Zygosity
Zygosity refers to the similarity of alleles for a trait in an organism. If both alleles are the same, the organism is homozygous for the trait. If both alleles are different, the organism is heterozygous for that trait...

 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
Gray (horse)
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...

 coat color, which also begins with intermixed white and colored hairs, roans do not become progressively lighter in color as they age.

Identification

Horses with the roan pattern have an even mixture of white and colored hairs in the coat. These interspersed white hairs are more scattered or absent on the horse's head, mane, tail, and lower legs. The unaffected color on the legs often forms a sharp, inverted "V" above the knee and hock, not seen in other roan-like coat patterns. The non-white background coat may be any color, as determined by unrelated genetic factors
Equine coat color genetics
Equine coat color genetics determine a horse's coat color. There are many different coat colors possible, but all colors are produced by the action of only a few different genes. The simplest genetic default color of all domesticated horses can be described as either "red" or "non-red", depending...

.

Often, the background coat color is used in combination with the word "roan" to describe the shade of a roan horse's coat, such as bay roan or gold champagne
Champagne gene
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...

 roan. However, there are also colloquial terms used for some colors. The most common terms for various roan colors are the following:

  • Blue roan, is loosely applied to any roan with a dark underlying coat that gives it a bluish cast. But in the strictest sense, "blue roan" is a common synonym for a roan with a black
    Black (horse)
    Black is a hair coat color of horses in which the entire hair coat is black. Black is a relatively uncommon coat color, and novices frequently mistake dark chestnuts or bays for black. However, some breeds of horses, such as the Friesian horse, Murgese and Ariegeois are almost exclusively black...

     background coat.
  • Red roan used to include both chestnut and bay roans. In 1999, the American Paint Horse
    American Paint Horse
    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 changed its coat color descriptions: roans with a chestnut background coat are registered "red roan", while "bay roan" is its own category. The American Quarter Horse
    American Quarter Horse
    The American Quarter Horse is an American breed of horse that excels at sprinting short distances. Its name came from its ability to outdistance other breeds of horses in races of a quarter mile or less; some individuals have been clocked at speeds up to 55 mph...

     Association followed suit in 2003. Previously, the term Strawberry roan described the pinkish color of a light chestnut or sorrel
    Sorrel (horse)
    Sorrel is an alternative word for one of the most common equine coat colors in horses. While the term is usually used to refer to a copper-red shade of chestnut, in some places it is used generically in place of "chestnut" to refer to any reddish horse with a same-color or lighter mane and tail,...

     roan. While less common, the term lilac roan may be applied to a dark chestnut roan, and honey roan to palomino
    Palomino
    Palomino is a coat color in horses, consisting of a gold coat and white mane and tail. Genetically, the palomino color is created by a single allele of a dilution gene called the cream gene working on a "red" base coat...

    s or the lightest sorrels.
  • Bay roan replaced red roan as the term for a roan with a bay background coat.


Some roan horses have more white hair than others, and even individual horses may look lighter or darker based on the season and their coats may vary from year to year. While roan is always present at birth, the soft first coat of newborn foals may not show the white hairs well. Some roan horses get darker with age. Generally, roans appear to have more white hair when they have their short summer coats and darker when they have their winter coats. These peculiar tendencies of roans led to the Icelandic
Icelandic language
Icelandic is a North Germanic language, the main language of Iceland. Its closest relative is Faroese.Icelandic is an Indo-European language belonging to the North Germanic or Nordic branch of the Germanic languages. Historically, it was the westernmost of the Indo-European languages prior to the...

 word for roan, which translates as "always changing color."

Roans have other unusual characteristics. If the skin is damaged by even a very minor scrape, cut or brand
Livestock branding
Livestock branding is a technique for marking livestock so as to identify the owner. Originally, livestock branding only referred to a hot brand for large stock, though the term is now also used to refer to other alternative techniques such as freeze branding...

, the coat grows back in solid-colored without any white hairs. These regions of solid-colored coat are called "corn spots" or "corn marks" and can appear even without the horse having had a visible injury. Another trait is reverse dappling; many horses develop rings of hair that appear slightly different-colored, called dapple
Dapple
Dapple may refer to:* Dapple, a book by Eleanor Arnason* DAPPLE Project, a pollution study* Dapple gray, a type of coat colour seen on horses* Silver dapple gene, also known as the "Z" gene, that dilutes the black base coat color in horses...

s, which often indicate good health. Usually dapples are darker than the surrounding coat, but on a roan, the dapples are lighter.

Terminology

In the most general sense, the word "roan" refers to any animal with a mixture of white and colored hairs in the coat. Recent research into equine coat color genetics
Equine coat color genetics
Equine coat color genetics determine a horse's coat color. There are many different coat colors possible, but all colors are produced by the action of only a few different genes. The simplest genetic default color of all domesticated horses can be described as either "red" or "non-red", depending...

 indicates that "true roan" or "classic roan" is distinct from several similar patterns which are collectively called "roaning." In studies of the white patterning genotypes of laboratory mice, no fewer than four produced roaning or flecking. Therefore, the existence of other types of roaning conditions not covered by those mentioned here is possible and likely. The patterns identified as "roaning" have particular qualities that can be used to tell them apart from true roan.

Roan mimics

Gray vs. roan


Roans are sometimes mistaken for grays
Gray (horse)
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...

. However, grays lighten with age, while roans do not. Gray is one of the most common coat colors found in horses, and is found in almost all breeds. The defining characteristic of the gray coat is that it becomes progressively lighter over time. Gray foal
Foal
A foal is an equine, particularly a horse, that is one year old or younger. More specific terms are colt for a male foal and filly for a female foal, but these terms are used until the horse is age three or four. When the foal is nursing from its dam , it may also be called a suckling...

s may be born any color, and there may be no indication of the future gray coat at birth. Mature grays may retain none of their original coat color, and have a "white
White (horse)
White horses are born white and stay white throughout their life. White horses may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white genes, are rare...

" coat, while the color of the skin and eyes
Equine vision
The equine eye is the largest of any land mammal. Its visual abilities are directly related to the animal's behavior and the fact that the horse is a flight animal...

 is unchanged. The first white hairs are usually seen around the muzzle and eyes. As a gray may go from entirely colored to entirely white over the course of his life, the process of "graying out" can, at times, closely resemble roan. Thoroughbred
Thoroughbred
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...

 and Arabian horse
Arabian horse
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...

s registered as "roan" are often gray, especially chestnuts
Chestnut (coat)
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. Genetically and visually, chestnut is characterized by the absolute absence of true black hairs...

 turning gray. Unlike grays, roans do not develop more white hair with age, and without white markings, roans retain colored heads.

Dun vs. roan

Blue dun or grullo
Grullo
Grullo is a color of horses in the dun family, characterized by tan-gray or mouse-colored hairs on the body, often with shoulder and dorsal stripes and black barring on the lower legs. In this coloration each individual hair is mouse-colored, unlike a roan which is composed of a mixture of dark and...

 (also grulla, mouse dun) coloring is created by the dun gene
Dun gene
The dun gene is a dilution gene that affects both red and black pigments in the coat color of a horse. The dun gene has the ability to affect the appearance of all black, bay, or chestnut -based horses to some degree by lightening the base body coat and suppressing the underlying base color to the...

 acting on a black
Black (horse)
Black is a hair coat color of horses in which the entire hair coat is black. Black is a relatively uncommon coat color, and novices frequently mistake dark chestnuts or bays for black. However, some breeds of horses, such as the Friesian horse, Murgese and Ariegeois are almost exclusively black...

 base coat, is a coat color with a bluish cast and darker points. Unlike blue roans, grullos are solid color and appear bluish due to low amounts of pigment
Melanin
Melanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...

 in each hair, not interspersed white hairs. Like other dun coat colors, grullos have dark or black primitive markings
Primitive markings
Primitive markings among domestic horses are a group of hair coat markings and qualities associated with primitive breeds, and the dun coat color family in particular. All dun horses possess at least the dorsal stripe but the presence of the other primitive markings varies...

, always including a stripe down the back.

Rabicano vs. roan

One pattern of roaning is rabicano
Rabicano
Rabicano, also called white ticking, is a horse coat color characterized by limited roaning in a specific pattern: interspersed white hairs most dense and originating from the flank and the tailhead...

, also called white ticking. While true roans have an even intermixture of white hairs throughout the body, except the extremities, the white hairs of a rabicano are densest around the base of the tail and the flank. Rabicano roaning frequently forms rings of white hair around the base of the tail, and in extensively roaned rabicanos, the white hairs may converge to form vertical stripes over the ribcage. Rabicano is found in many breeds, and may account for some "roan" Arabians
Arabian horse
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...

.

Sabino vs. roan

Roaning is also associated with some of the sabino
Sabino horse
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 gene, for which there is a DNA test...

 white spotting patterns. There are many patterns in many breeds called "sabino," and these patterns usually feature irregular, rough-edged patches of white that originate from the lower legs, face, and ventral midline. The borders of these white patches can be heavily roaned, and some sabinos can be mistaken for roans. The roaning of sabinos will originate in a white patch, and the roaning is uneven.

Varnish roan vs. roan

The leopard complex
Leopard complex
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...

 colors, characteristic of the Appaloosa
Appaloosa
The Appaloosa is a horse breed best known for its colorful leopard-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...

 breed, have several manifestations that feature mixtures of white and colored hairs. A varnish roan
Varnish roan
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...

, one type of leopard complex coat color also called "marble", is an all-over blend of white and colored hairs. Patches of skin that lie close to the bone, such as on the face and legs, and the point of shoulder and point of hip, do not grow as much white hair. These darker patches are called "varnish marks" and are not found in true roans. Varnish roans can also be distinguished from true roans by the presence of leopard complex characteristics, such as the white sclera
Sclera
The sclera , also known as the white or white of the eye, is the opaque , fibrous, protective, outer layer of the eye containing collagen and elastic fiber. In the development of the embryo, the sclera is derived from the neural crest...

, finely striped hooves
Horse hoof
A horse hoof is a structure surrounding the distal phalanx of the 3rd digit of each of the four limbs of Equus species, which is covered by complex soft tissue and keratinised structures...

, and mottled skin around the eyes, muzzle, and genitals.

Prevalence

True or classic roan is common in European draft
Draft horse
A draft horse , draught horse or dray horse , less often called a work horse or heavy horse, is a large horse bred for hard, heavy tasks such as ploughing and farm labour...

 breeds such as the Brabant
Belgian (horse)
The Belgian Draft horse or Belgian, also known as Belgian Heavy Horse, Brabançon, or Brabant, is a draft horse breed from the Brabant region of modern Belgium, where it is called the or Flemish: . It is one of the strongest of the heavy breeds...

, Ardennes
Ardennes (horse)
The Ardennes or Ardennais is one of the oldest breeds of draft horse, and originates from the Ardennes area in Belgium, Luxembourg and France. They are heavy-boned with thick legs and are used for draft work. The Ardennes is found in many colors, although black horses are very rare and are not...

, Trait Du Nord
Trait Du Nord
The Trait du Nord, previously known also as Ardennais du Nord or Ardennais de type Nord, is a breed of heavy draft horse developed and bred in the area of Hainaut in western Belgium and in north-eastern France. Originally considered a sub-type of the Ardennes, it became an individual breed with the...

, Italian Heavy Draft
Italian Heavy Draft
The Italian Heavy Draft, or Rapid Heavy Draft, is a breed of draft horse from Italy. The full Italian name of the breed is Cavallo Agricolo Italiano da Tiro Pesante Rapido, "Italian Rapid Heavy Draft Farm Horse", and the abbreviation TPR ) is often used.Generally chestnut in color, the breed is...

, and Rhenish-German Cold-Blood
Rhenish-German Cold-Blood
The Rhenish-German Cold-Blood is a big horse which comes from Germany. This cold-blood was very popular in its heyday at the beginning of the 20th century, but now there are fewer uses.-History:...

. It is also found regularly in North American breeds like the Quarter Horse
American Quarter Horse
The American Quarter Horse is an American breed of horse that excels at sprinting short distances. Its name came from its ability to outdistance other breeds of horses in races of a quarter mile or less; some individuals have been clocked at speeds up to 55 mph...

, Paint Horse
American Paint Horse
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...

, Peruvian Paso
Peruvian Paso
The Peruvian Paso or Peruvian Horse is a breed of light pleasure saddle horse known for its smooth ride. It is distinguished by a natural, four-beat, lateral gait called the paso llano.-History:...

, Paso Fino
Paso Fino
The Paso Fino is a naturally gaited light horse breed dating back to horses imported to the Caribbean from Spain. Pasos are prized for their smooth, natural, four beat, lateral ambling gait and are used in many disciplines, but are especially popular for trail riding...

, Standardbred, Spanish Mustang
Spanish Mustang
The Spanish Mustang is a horse breed of historical importance. They descend from horses introduced from Spain during the early conquest of the Americas. They are a type that today is mostly or wholly now extinct in Spain...

, and Tennessee Walking Horse.

British ponies such as Dales Ponies
Dales Pony
-External links:****...

, Welsh Ponies
Welsh Pony
The Welsh Pony and Cob are closely related horse breeds including both pony and cob types, which originated in Wales in the United Kingdom...

, Gypsy Cobs
Gypsy Vanner horse
The Gypsy Horse , also known as an Irish cob , Gypsy Cob, Gypsy Vanner , Coloured Cob or Tinker horse , is a horse breed. The breed originates from the UK and Ireland...

, Shetland Ponies
Shetland pony
The Shetland pony is a breed of pony originating in the Shetland Isles. Shetlands range in size from a minimum height of approximately 28 inches to an official maximum height of 42 inches at the withers. Shetland ponies have heavy coats, short legs and are considered quite intelligent...

, Connemara ponies
Connemara pony
The Connemara pony is a pony breed originating in Ireland. They are known for their athleticism, versatility and good disposition. The breed makes excellent show ponies.-History:...

, and New Forest ponies
New Forest pony
The New Forest Pony or New Forester is one of the recognised Mountain and moorland or Native pony breeds of the British Isles. The breed is valued for its hardiness, strength and sureness of foot...

 may be roan. Icelandic horse
Icelandic horse
The Icelandic horse is a breed of horse developed in Iceland. Although the horses are small, at times pony-sized, most registries for the Icelandic refer to it as a horse. Icelandic horses are long-lived and hardy. In their native country they have few diseases; Icelandic law prevents horses from...

s and Miniature horse
Miniature horse
Miniature horses are found in many nations, particularly in Europe and the Americas. The designation of miniature horse is determined by the height of the animal, which, depending on the particular breed registry involved, is usually less than as measured at the last hairs of the mane, which are...

s may also be roan. Some roan Trakehner
Trakehner
Trakehner is a light warmblood breed of horse, originally developed at the East Prussian state stud farm in the town of Trakehnen from which the breed takes its name...

s and American Saddlebred
American Saddlebred
The American Saddlebred, formerly known as the American Saddle Horse, is a breed of horse that was developed in Kentucky by plantation owners. Today, in the horse show world, they are most commonly seen under saddle in Saddle seat style riding, and in various types of driving, including pleasure...

s are known. The Hokkaido Pony
Hokkaido Pony
The Hokkaido pony, generally called Do-san-ko as a term of endearment, is an old but rare breed of pony native to Japan.-History:The Hokkaido pony is thought to have been brought to Hokkaidō from Honshū by fishermen during the Edo period...

 of Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

 may also be roan.

True roan has not been satisfactorily identified in Arabians
Arabian horse
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...

 or Thoroughbred
Thoroughbred
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...

s. Despite this, Thoroughbreds and Arabians with roan-like coats are sometimes registered as "roan." Thoroughbred "roans" are described by the Jockey Club
Jockey Club
The Jockey Club is the largest commercial organisation in British horseracing. Although no longer responsible for the governance and regulation of the sport, it owns 14 of Britain's famous racecourses, including Aintree, Cheltenham and Newmarket, amongst other concerns such as the National Stud and...

 as a mixture of white with red or brown hairs, but which researchers identify as chestnuts turning gray
Gray (horse)
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...

. The Arabian Horse Association defines "roan" as an even mixture of white and colored, usually chestnut, hairs, but researchers suggest this may actually be a unique type of white pattern, probably rabicano, or, occasionally, minimally expressed sabino.

Genetics

Roan is a simple dominant
Dominance relationship
Dominance in genetics is a relationship between two variant forms of a single gene, in which one allele masks the effect of the other in influencing some trait. In the simplest case, if a gene exists in two allelic forms , three combinations of alleles are possible: AA, AB, and BB...

 trait symbolized by the Rn allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...

. Traits that are dominantly-inherited cannot skip generations, meaning that two non-roan parents cannot produce a roan offspring. In cases where roan has appeared to skip generations, one of the parents is usually discovered to be slightly roaned. A roan can also be born from two seemingly non-roan parents if the roan coat is "masked" by extensive white markings or gray
Gray (horse)
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...

. In some cases, the supposedly roan offspring is not true roan at all, but rabicano, sabino, or influenced by some other genetic factor.

The University of California, Davis
University of California, Davis
The University of California, Davis is a public teaching and research university established in 1905 and located in Davis, California, USA. Spanning over , the campus is the largest within the University of California system and third largest by enrollment...

 School of Veterinary Medicine's genetics services have developed a DNA test that uses genetic marker
Genetic marker
A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify cells, individuals or species. It can be described as a variation that can be observed...

s to indirectly determine the number of Rn or rn alleles a horse has. The mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

 responsible for true roan has not yet been identified exactly, but been assigned to equine chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...

 3 (ECA3) in the KIT sequence. A the roan zygosity test is reliable for American Quarter Horse
American Quarter Horse
The American Quarter Horse is an American breed of horse that excels at sprinting short distances. Its name came from its ability to outdistance other breeds of horses in races of a quarter mile or less; some individuals have been clocked at speeds up to 55 mph...

, American Paint Horse
American Paint Horse
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...

, Welsh Pony
Welsh Pony
The Welsh Pony and Cob are closely related horse breeds including both pony and cob types, which originated in Wales in the United Kingdom...

, and Gypsy Cob
Gypsy Vanner horse
The Gypsy Horse , also known as an Irish cob , Gypsy Cob, Gypsy Vanner , Coloured Cob or Tinker horse , is a horse breed. The breed originates from the UK and Ireland...

. Until a direct test is developed, the roan zygosity test may enable breeders to produce roans more reliably.

Homozygous roan

A 1979 study of American-bred Belgian draft horses
Belgian (horse)
The Belgian Draft horse or Belgian, also known as Belgian Heavy Horse, Brabançon, or Brabant, is a draft horse breed from the Brabant region of modern Belgium, where it is called the or Flemish: . It is one of the strongest of the heavy breeds...

 found fewer roan offspring from roan-to-roan matings than expected for a simple dominant trait. Finding neither stillborn nor sickly, short-lived foals from these roan parents, the researchers concluded that in the homozygous
Zygosity
Zygosity refers to the similarity of alleles for a trait in an organism. If both alleles are the same, the organism is homozygous for the trait. If both alleles are different, the organism is heterozygous for that trait...

 condition the roan gene was lethal to the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

 or fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...

. Other studies at the time were using progeny ratios to identify potential lethality related to other coat colors, such as "dominant white
Dominant white
Dominant white is a group of genetically related coat color conditions in the horse, best known for producing an all-white coat, but also for producing some forms of white spotting and white markings. Dominant white horses are born with unpigmented pink skin and white hair with dark eyes, although...

" and "lethal white
Lethal white syndrome
Lethal white syndrome , also called overo lethal white syndrome , lethal white overo , and overo lethal white foal syndrome , is an autosomal genetic disorder most prevalent in the American Paint Horse...

," and so roan was believed to follow a similar pattern. Genetic science in the 1970s could not provide a clear answer, as methods of molecular analysis
Genetic analysis
Genetic analysis can be used generally to describe methods both used in and resulting from the sciences of genetics and molecular biology, or to applications resulting from this research....

 had not yet been developed.

"Lethal roan" persisted until recently, when homozygous roan stallions with large numbers of offspring - all roan - were satisfactorily identified. Homozygous roan stallions were identified in both European populations of Belgian drafts in 1977, and in North American Quarter Horse
American Quarter Horse
The American Quarter Horse is an American breed of horse that excels at sprinting short distances. Its name came from its ability to outdistance other breeds of horses in races of a quarter mile or less; some individuals have been clocked at speeds up to 55 mph...

 stallions.

In some breeds, homozygous roans can be identified by an indirect DNA marker
Genetic marker
A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify cells, individuals or species. It can be described as a variation that can be observed...

 test. Such horses, with the genotype
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...

 Rn/Rn, produce 100% roan offspring. Homozygous roans and heterozygous roans (Rn/rn) are identical in appearance.

Equine linkage group II

During the production of sex cells, DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 is "reshuffled" to ensure that the next generation does not inherit, for example, grandpa's chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...

 8, but a mixture of DNA from each parent. Instead, paired chromosomes exchange parallel pieces of DNA, a process called chromosomal crossover
Chromosomal crossover
Chromosomal crossover is an exchange of genetic material between homologous chromosomes. It is one of the final phases of genetic recombination, which occurs during prophase I of meiosis in a process called synapsis. Synapsis begins before the synaptonemal complex develops, and is not completed...

, prior to being passed on to the next generation. When particular gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

s are located physically close together on a chromosome, they tend to be passed on together. The rate at which two genes are passed on together can be used to calculate their distance
Centimorgan
In genetics, a centimorgan or map unit is a unit of recombinant frequency for measuring genetic linkage, defined as that distance between chromosome positions for which the expected average number of intervening chromosomal crossovers in a single generation is 0.01. It is often used to infer...

 from each other on the chromosome. Genes which tend to be passed on as a group form what is called a "linkage group
Genetic linkage
Genetic linkage is the tendency of certain loci or alleles to be inherited together. Genetic loci that are physically close to one another on the same chromosome tend to stay together during meiosis, and are thus genetically linked.-Background:...

."

Equine linkage group II includes a number of genes. The first linkage was found between a blood type
Blood type
A blood type is a classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells . These antigens may be proteins, carbohydrates, glycoproteins, or glycolipids, depending on the blood group system...

 marker
Genetic marker
A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify cells, individuals or species. It can be described as a variation that can be observed...

 and tobiano
Tobiano
Tobiano is a spotted color pattern commonly seen in Pinto horses, produced by a dominant gene. The tobiano gene produces white-haired, pink-skinned patches on a base coat color. The coloration is present from birth and does not change throughout the horse's lifetime, unless the horse also carries...

 white spotting in 1978. The same blood type marker, albumin
Albumin
Albumin refers generally to any protein that is water soluble, which is moderately soluble in concentrated salt solutions, and experiences heat denaturation. They are commonly found in blood plasma, and are unique to other blood proteins in that they are not glycosylated...

, was linked to another blood protein called vitamin D-binding protein. In 1982, a linkage grouping was proposed, including three genes for serum
Serum
Serum may refer to:*Blood serum, a component of blood which is collected after coagulation.**Antiserum, blood serum with specific antibodies for passive immunity*Serous fluid, any clear bodily fluid*any drug derived from an animal's blood or serous fluid...

 protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s, and three for coat color
Equine coat color
Horses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them.While most horses remain the same color throughout life, a few, over the course of several years, will develop a different coat color from that with which they were born...

: tobiano spotting, chestnut
Chestnut (coat)
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. Genetically and visually, chestnut is characterized by the absolute absence of true black hairs...

, and roan. Research since equine linkage group II was defined has identified the exact location of the tobiano allele and the chestnut allele. The region of the chromosome that harbors the roan gene is homologous to parts of chromosomes in other species that also control coat color, even some similar to roan. Presently, the KIT
CD117
Mast/stem cell growth factor receptor also known as proto-oncogene c-Kit or tyrosine-protein kinase Kit or CD117 is a protein that in humans is encoded by the KIT gene...

gene is the primary candidate gene for roan. While a chromosomal inversion
Chromosomal inversion
An inversion is a chromosome rearrangement in which a segment of a chromosome is reversed end to end. An inversion occurs when a single chromosome undergoes breakage and rearrangement within itself. Inversions are of two types: paracentric and pericentric.Paracentric inversions do not include the...

 of KIT causes tobiano
Tobiano
Tobiano is a spotted color pattern commonly seen in Pinto horses, produced by a dominant gene. The tobiano gene produces white-haired, pink-skinned patches on a base coat color. The coloration is present from birth and does not change throughout the horse's lifetime, unless the horse also carries...

 white spotting, KIT also harbors one or more allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...

s responsible for sabino
Sabino horse
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 gene, for which there is a DNA test...

 spotting, no fewer than eleven alleles responsible for dominant white
Dominant white
Dominant white is a group of genetically related coat color conditions in the horse, best known for producing an all-white coat, but also for producing some forms of white spotting and white markings. Dominant white horses are born with unpigmented pink skin and white hair with dark eyes, although...

 spotting, and is thought to be a major contributor to many other forms of less distinctive white markings
Horse markings
Markings on horses usually are 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...

.

The effect of linkage between roan and chestnut is readily observed. If a horse possesses one chromosome with the wildtype non-chestnut allele and the dominant roan allele (E and Rn), while the other chromosome contains the recessive chestnut allele and the recessive non-roan allele (e and rn), he will outwardly appear blue roan, barring the influence of other genes. Normally, the chestnut and roan alleles would be separated during chromosomal crossover, but these two linked genes will usually remain together. Such a horse will produce sex cells that are either E/Rn or e/rn. Mated to chestnut
Chestnut (coat)
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. Genetically and visually, chestnut is characterized by the absolute absence of true black hairs...

non-roan partners (e/rn), the horse would produce primarily blue roans, or chestnut non-roans, but few chestnut roans and few black non-roans. If, on the other hand, the recessive e and dominant Rn were on the same chromosome, the horse would be expected to produce primarily chestnut roans and non-chestnut non-roans with chestnut, non-roan partners.
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