Roan is a coat color found in many animals, notably horse

Horse

The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...

s, cattle

Cattle

Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...

 and dog

Dog

The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...

s. It is defined generally as an even mixture of white and pigmented hairs that does not "gray out"

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...

 or fade as the animal ages. There are a variety of genetic conditions which produce the colors described as "roan" in various species.

Roan horses

A horse with intermixed white and colored hairs of any color is usually called a roan. However, such mixtures, which can appear superficially similar, are caused by a number of separate genetic

Introduction to genetics

Genetics is the study of genes, and tries to explain what they are and how they work. Genes are how living organisms inherit features from their ancestors; for example, children usually look like their parents because they have inherited their parents' genes...

 factors. Identifiable types of roans include true or classic roan

Roan (horse)

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 more solid-colored. The roan pattern is dominantly-inherited, and is found in many horse breeds...

, 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...

, and 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...

, though other currently unknown factors may be responsible for ambiguous "roaning." 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...

 horses, which become lighter as they age until their hair coat is nearly completely white, may be confused with roans when they are young. Duns

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...

, which are solid-colored horses affected by the dun dilution factor

Dilution gene

Dilution gene is a popular term for 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:-General:...

 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

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...

 under the control of other genes, the head, mane, tail, and lower legs are dark. 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...

. 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...

 21 (ECA21) in the KIT sequence. The overall effect is that of a silver or lightened appearance to the affected part of the coat.

Descriptions of roan coat colors

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...

 are as follows:

• Red Roan or Strawberry Roan describes true or classic roan on a 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...
  
   base coat. The mane and tail remain red or have only a few white hairs, while the body ranges from nearly chestnut to pinkish. Geneticists prefer the term "chestnut roan," but this term is not in common use.
• Bay Roan is true roan on a bay coat. The particular shade depends on the underlying shade of bay; but the mane, tail, and lower legs are black, and the reddish body is intermingled with white hairs. The head is usually red. Formerly, bay roans were lumped together with chestnut roans and both called "red roans."
• Blue Roan is true roan 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...
  
   coat. The mane, tail, head, and legs remain black, while the body takes on a grayish or bluish appearance. Blue 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...
  
   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...
  
  s. However, Grays fade with age, while roans do not; and grullos are blue duns
  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...
  
   and possess dun markings but not intermingled white hairs.

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.

Roan mimics

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...

 is not a true roan; it is actually one of 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...

 coat patterns associated with 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...

, Knabstrupper, Noriker horse

Noriker horse

The Noriker horse, also called the Norico-Pinzgauer and historically known as the Pinzgauer horse, is a moderately heavy Austrian draught horse breed. The Noriker is considered indigenous to the central Alpine region of Europe, and is believed to have originated around the highest mountain of...

 and related breeds. 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...

 is a white pattern that falls into the category of roaning or scattered white hairs, the genetics of which are not yet fully understood. Sometimes called ticking, rabicano is common even in breeds that do not have true or classic roan, including Arabians and 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. 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. Some forms of 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...

, which is a pinto

Pinto horse

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...

 pattern, have roaning along the edges of other white spots or 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...

  A roan horse 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.

Roan dogs

The genetics behind roan dogs are still unclear, and at present candidate genes have been ruled out. 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 Spaniel

English Cocker Spaniel

The English Cocker Spaniel is a breed of gun dog. The English Cocker Spaniel is an active, good-natured, sporting dog, standing well up at the withers and compactly built. There are "field" or "working" cockers and "show" cockers...

s, American Cocker Spaniel

American Cocker Spaniel

The American Cocker Spaniel is a breed of sporting dog. It is a spaniel type dog that is closely related to the English Cocker Spaniel; the two breeds diverged during the 20th century due to differing breed standards in America and the UK...

s, English Springer Spaniel

English Springer Spaniel

The English Springer Spaniel is a breed of gun dog traditionally used for flushing and retrieving game. It is an affectionate, excitable breed with an average lifespan of twelve to fourteen years. Descended from the Norfolk or Shropshire Spaniels of the mid-19th century, the breed has diverged into...

s, Field Spaniel

Field Spaniel

The Field Spaniel is a medium-sized breed dog of the spaniel type. They were originally developed to be all black show dogs in the late 19th and early 20th centuries and were unpopular for work as a hunting dog. However during the mid 20th century they were redeveloped as a longer legged dog that...

s and Brittanys

Brittany (dog)

The Brittany is a breed of gun dog bred primarily for bird hunting. Although the Brittany is often referred to as a Spaniel, the breed's working characteristics are more akin to those of a pointer or setter.-History:...

, German Shorthaired Pointer

German Shorthaired Pointer

The German shorthaired pointer is a breed of dog developed in the 19th century in Germany for hunting.The breed is streamlined yet powerful with strong legs that make it able to move rapidly and turn quickly. It has moderately long floppy ears set high on the head. Its muzzle is long, broad, and...

s, Spinoni Italiani

Spinone Italiano

The Spinone Italiano is an Italian dog breed. However, it should be recognized that the Spinone is a unique, indivisable breed and the correct reference is Spinone . It was originally bred as a versatile gun dog. To this day, the breed still masters that purpose...

, Lagotto Romagnolo

Lagotto Romagnolo

The Lagotto Romagnolo is a breed of dog that comes from the Romagna sub-region of Italy. The name means "lake dog from Romagna," coming from the Italian word lago, lake. Its traditional function is a gundog, specifically a water retriever...

s and English Setter

English Setter

The English Setter is a breed of dog. It is part of the Setter family, which includes red Irish Setters, Irish Red and White Setters, and black-and-tan Gordon Setters. It is a gun dog, bred for a mix of endurance and athleticism.- Appearance :...

s, as well as Border Collie

Border Collie

The Border Collie is a herding dog breed developed in the Anglo-Scottish border region for herding livestock, especially sheep. It is the most widespread of the collie breeds....

s and many other breeds.

In dogs, roan manifests itself only in unpigmented areas, the presence and shape of which are determined by other genes. 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. 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. 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. The term belton is reserved for English Setter

English Setter

The English Setter is a breed of dog. It is part of the Setter family, which includes red Irish Setters, Irish Red and White Setters, and black-and-tan Gordon Setters. It is a gun dog, bred for a mix of endurance and athleticism.- Appearance :...

s.

In 1957, Little suggested that roan and ticking were controlled separately, and postulated that roan may have been homologous to "silvered" coat in mice. This condition in mice is actually homologous to merle

Merle (coat colour in dogs)

Merle is a pattern in a dogs coat, though is commonly incorrectly referred to as a color.- Description :Merle can affect all coat colors but the colors most commonly seen that are affected are brown and black, when affected by merle they are usually called liver and blue, though some call liver red...

, which might be described by some as "roan." 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.

Roan cattle

Breeds of cattle

Cattle

Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...

 known for roans are the Belgian Blue

Belgian Blue

thumb|right|Belgian Blue bullthumb|right|Belgium Blue cow with the scars from [[caesarean sections]] clearly visible.Belgian Blue cattle are a beef breed from Belgium, known in French as . Alternative names include Belgian Blue-White, Belgian White and Blue Pied, Belgian White Blue, Blue and Blue...

 and Shorthorn

Shorthorn

The Shorthorn breed of cattle originated in the North East of England in the late 18th century. The breed was developed as dual purpose, suitable for both dairy and beef production; however there were always certain blood lines within the breed which emphasised one quality or the other...

. 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, which are genetically separate from roan. As a result, most roan cows exhibit blotches of clearly colored and clearly white hair, with roan patches. Some "cryptic" roan cattle appear solid, but upon close inspection reveal a small roan patch. 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

Charolais cattle

Charolais cattle are a beef breed of cattle which originated in Charolais, around Charolles, in France. They are raised for their meat and are known for their composite qualities when crossed with other breeds, most notably Angus and Hereford cattle...

 and White Park

White Park

The White Park is a rare breed of horned cattle with ancient herds preserved in Great Britain.-Description:...

 breeds is not related to roan.

Roan in Shorthorns and Belgian Blues is controlled by the mast cell growth factor (MGF) 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...

, also called the steel locus, on bovine 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...

 5. Part of the KIT ligand

Stem cell factor

Stem Cell Factor is a cytokine that binds to the c-Kit receptor . SCF can exist both as a transmembrane protein and a soluble protein...

, this region is involved in many cell differentiation processes

Cellular differentiation

In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a simple zygote to a complex system of...

. Mast cell growth factor promotes 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...

 production by pigment cells

Melanocyte

-External links: - "Eye: fovea, RPE" - "Integument: pigmented skin"...

, 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

Recessive

In genetics, the term "recessive gene" refers to an allele that causes a phenotype that is only seen in a homozygous genotype and never in a heterozygous genotype. Every person has two copies of every gene on autosomal chromosomes, one from mother and one from father...

), 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.

The reproductive condition "White Heifer Disease," associated with the MGF gene, is characterized by homozygous MGF-white heifers with incomplete reproductive tracts.

Roan Guinea Pigs

The roan coloration

Domestic varieties of guinea pigs

There are many breeds of Guinea pig which have been developed since its domestication ca. 5000 BC. Breeds vary widely in appearance and purpose, ranging from show breeds with long, flowing hair to those in use as model organisms by science. From ca...

 of Guinea pig

Guinea pig

The guinea pig , also called the cavy, is a species of rodent belonging to the family Caviidae and the genus Cavia. Despite their common name, these animals are not in the pig family, nor are they from Guinea...

s is linked to microphthalmia

Microphthalmia

Microphthalmia also referred to as microphthalmos, nanophthalmia or nanophthalmos, is a developmental disorder of the eye that literally means small eye...

. 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. This is not to be confused with the 'Magpie' variety, which is a brindled guinea pig lacking red pigment due to the "chinchilla" allele also responsible for self white and silver agouti coloration.

About 25% of guinea pigs born to a mating of two roans are completely white, with a constellation of deformities called lethal white syndrome, although it has no relation to Overo Lethal White Syndrome in horses or double merle syndrome in dogs. These symptoms include:

• Partial or complete blindness
  Blindness
  Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...
  
  
• Partial or complete deafness
• Microphthalmia
  Microphthalmia
  Microphthalmia also referred to as microphthalmos, nanophthalmia or nanophthalmos, is a developmental disorder of the eye that literally means small eye...
  
   or anophthalmia
  Anophthalmia
  Anophthalmia, also known as anophthalmos , is the congenital absence of one or both eyes.-Prevalence:...
  
  
• Unpigmented eyes
• Missing or deformed incisor
  Incisor
  Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
  
  s
• Deformed molars
  Molar (tooth)
  Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
  
  
• Elongated tooth
  Tooth
  Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...
  
   roots
• Malabsorption in the small intestine, due in some cases to lack of intestinal villi
• Increased susceptibility to illness
  Illness
  Illness is a state of poor health. Illness is sometimes considered another word for disease. Others maintain that fine distinctions exist...
  
  

It is worth noting that, unlike anophthalmic

Anophthalmia

Anophthalmia, also known as anophthalmos , is the congenital absence of one or both eyes.-Prevalence:...

hamsters, lethal white guinea pigs are not sterile. Females may be unable to deliver live young.

Lethal white guinea pigs have a decreased lifespan in general, although individuals have reportedly lived to 6 or 7 years. Many die shortly after birth or at weaning age. With hand-feeding and regular dental care, lethals can live 2–3 years.

External links

Dogs

• Photos of roan English Cockers