Genes associated with coat color
Each hair follicle is surrounded by many melanocytes (pigment cells), which make and transfer the pigmentPigment shade
Several loci can be grouped as affecting the shade of color: the Brown (B), Dilution (D), and Intensity (I) loci.B (brown) locus
The gene at the B locus is known as tyrosinase related protein 1 (TYRP1). This gene affects the color of the eumelanin pigment produced, making it either black or brown. TYRP1 is an enzyme involved in the synthesis of eumelanin. Each of the known mutations appears to eliminate or significantly reduce TYRP1 enzymatic activity. This modifies the shape of the final eumelanin molecule, changing the pigment from a black to a brown color. Color is affected in coat and skin (including the nose and paw pads). There are four known alleles that occur at the B locus: *''B'' = Black eumelanin. An animal that has at least one copy of the ''B'' allele will have a black nose, paw pads and eye rims and (usually) dark brown eyes. *''b'' = Brown eumelanin - such as chocolate or liver (includes several alleles - ''bs'', ''bd'' and ''bc''). An animal with any matched or unmatched pair of the ''b'' alleles will have brown, rather than black, hair, a liver nose, paw pads and eye rims, and hazel eyes. Phaeomelanin color is unaffected. Only one of the alleles is present in the English Setter (bs), Doberman Pinscher (''bd'') and Italian Greyhound (''bc''), but in most breeds with any brown allele two or all three are present. It is unknown whether the different brown alleles cause specific shades or hues of brown. ''B'' is dominant to ''b''.D (dilute) locus
The melanophilin gene (MLPH) at the D locus causes a dilution mainly of eumelanin, while phaeomelanin is less affected. This dilution gene determines the intensity of pigmentation. MLPH codes for a protein involved in the distribution of melanin - it is part of the melanosome transport complex. Defective MLPH prevents normal pigment distribution, resulting in a paler colored coat. There are two common alleles: ''D'' (normal, wild-type MLPH), and ''d'' (defective MLPH) that occur in many breeds. But recently the research group of Tosso Leeb has identified additional alleles in other breeds. *''D'' = Not diluted. Black or brown eumelanin (as determined by Brown locus), reddish or orangish tan phaeomelanin. *''d'' = Diluted. Diluted fur color: black eumelanin (''B/-'') diluted to bluish grey (ranging from light blue-grey to dark steel); brown eumelanin (''b/b'') diluted to taupe or "Isabella". Phaeomelanin is diluted from red to yellowish tan; this phaeomelanin dilution is not as dramatic as the eumelanin color shift. Slight to moderate dilution of the paw pads and eye rims towards bluish grey if ''B/-'' or taupe if ''b/b'', and slight to moderate reduction of eye color from brown towards amber in a ''B/-'' animal, or from hazel towards light amber in a ''b/b'' animal. ''D'' is completely dominant to ''d''. This dilution gene can occur in almost any breed, where blue gene is the most common. Also, there are some breeds that come in dilute but with no specific color, such as theColor gene interactions
I (intensity) locus
The alleles responsible forRed Pigment
Pigment Intensity for dogs who are darker than Tan (shades of gold to red) has been attributed to a mutation upstream of KITLG, in the same genes responsible for coat color in mice and hair color in humans. The mutation is the result of a Copy Number Variant, or duplication of certain instructions within a gene, that controls the distribution of pigment in a dog's hair follicle. As such, there are no genetic markers for red pigment. * Dogs with a higher CNV were observed to have darker, richer colors such as deep gold, red, and chestnut. * Dogs with a lower CNV were observed to have lighter gold and orange colors. This mutation not only effects Pheomelanin, but Eumelanin as well. This mutation does not effect all breeds the same.Pigment type
Several loci can be grouped as controlling when and where on a dog eumelanin (blacks-browns) or phaeomelanin (reds-yellows) are produced: the Agouti (A), Extension (E) and Black (K) loci. Intercellular signaling pathways tell a melanocyte which type of melanin to produce. Time-dependent pigment switching can lead to the production of a single hair with bands of eumelanin and phaeomelanin. Spatial-dependent signaling results in parts of the body with different levels of each pigment. MC1R (the E locus) is a receptor on the surface of melanocytes. When active, it causes the melanocyte to synthesize eumelanin; when inactive, the melanocyte produces phaeomelanin instead. ASIP (the A locus) binds to and inactivates MC1R, thereby causing phaeomelanin synthesis. DEFB103 (the K locus) in turn prevents ASIP from inhibiting MC1R, thereby increasing eumelanin synthesis.A (agouti) locus
The alleles at the A locus are related to the production of agouti signalling protein (ASIP) and determine whether an animal expresses an agouti appearance, and, by controlling the distribution of pigment in individual hairs, what type of agouti. There are four known alleles that occur at the A locus: * ''Ay'' = Fawn or sable. Tan with black whiskers and varying amounts of black-tipped and/or all-black hairs dispersed throughout. Fawn typically referring to dogs with clearer tan and sable to those with more black shading. * ''aw'' = Wild-type agouti. Each hair with 3-6 bands alternating black and tan. Also called wolf sable. * ''at'' = Tan point. Black with tan patches on the face and underside - including saddle tan (tan with a black saddle or blanket). Phaeomelanin production is limited to tan points; dark portions of the dog are solid eumelanin hairs. * ''a'' = Recessive black. Solid black, inhibition of phaeomelanin. * ''ayt'' = Recombinant fawn (expresses a varied phenotype depending on the breed) has been identified in numerous Tibetan Spaniels and individuals in other breeds, including the Dingo. Its hierarchical position is not yet understood. Most texts suggest that the dominance hierarchy for the A locus alleles appears to be as follows: ''Ay > aw > at > a''; however, research suggests the existence of pairwise dominance/recessiveness relationships in different families and not the existence of a single hierarchy in one family. * ''Ay'' is incompletely dominant to ''at'', so that heterozygous individuals have more black sabling, especially as puppies and ''Ayat'' can resemble the ''awaw'' phenotype. Other genes also affect how much black is in the coat. * ''aw'' is the only allele present in many Nordic spitzes, and is not present in most other breeds. * ''at'' includes tan point and saddle tan, both of which look tan point at birth. Modifier genes in saddle tan puppies cause a gradual reduction of the black area until the saddle tan pattern is achieved. * ''a'' is only present in a handful of breeds. Most black dogs are black due to the K locus allele KB for dominant black. Border Collies is one of the few breeds that lack agouti patterning, and only have sable and tan points. However, many border collies still test to have agouti genes.E (extension) locus
The alleles at the E locus (the melanocortin receptor one gene or ''MC1R'') determine whether an animal expresses aK (dominant black) locus
The alleles at the K locus (the β-Defensin 103 gene or DEFB103) determine the coloring pattern of an animal's coat. There are three known alleles that occur at the K locus: *''KB'' = Dominant black (black) *''kbr'' = Brindle (black stripes added to tan areas) *''ky'' = Phaeomelanin permitted (pattern expressed as per alleles present at A and E loci) The dominance hierarchy for the K locus alleles appears to be as follows: ''KB'' > ''kbr'' > ''ky''. *''KB'' causes a solid eumelanin coat (black, brown, grey or taupe) except when combined with ''e/e'' (tan or white), ''Eh/-'' (Cocker sable) or ''Em/- G/-'' and appropriate coat type (light eumelanin with dark eumelanin mask) *''kbr'' causes the addition of eumelanin stripes to all tan areas of a dog except when combined with ''e/e'' (no effect) or ''EG/- atat'' non-''KB/-'' (eumelanin and sabled areas become striped, tan areas remain tan) *''ky'' is wild-type allowing full expression of other genes.Interactions of some genes with brindle
Alleles at the Agouti (A), Extension (E) and Black (K) loci determine the presence or absence of brindle and its location:Patches and white spotting
The Merle (M), Harlequin (H), and Spotting (S) loci contribute to patching, spotting, and white markings. Alleles present at the Merle (M) and Harlequin (H) loci cause patchy reduction of melanin to half (merle), zero (harlequin) or both (double merle). Alleles present at the Spotting (S), Ticking (T) and Flecking (F) loci determine white markings.H (harlequin) locus
DNA studies have isolated a missense mutation in the 20S proteasome β2 subunit at the H locus. The H locus is a modifier locus (of the M locus) and the alleles at the H locus will determine if an animal expresses a harlequin vs merle pattern. There are two alleles that occur at the H locus: * ''H'' = Harlequin (if ''M/-'', patches of full colour and white) * ''h'' = Non-harlequin (if ''M/-'', normal expression of merle) ''H/h'' heterozygotes are harlequin and ''h/h'' homozygotes are non-harlequin. Breeding data suggests that homozygous ''H/H'' is embryonic lethal and that therefore all harlequins are ''H/h''. * The Harlequin allele is specific to Great Danes. Harlequin dogs (''H/h M/m'') have the same pattern of patches as merle (''h/h M/m'') dogs, but the patches are white andM (merle) locus
The alleles at the M locus (the silver locus protein homolog gene or= variation on merle allele
= There are other new discovery on M locus and it would be useful to add the supplementary category on "M(merle) Locus" part. Since the original section only talk about just one allele M, but there are some variation on the one allele and derive a number of new alleles, which will lead to the other production of pigment. * Cryptic merle (Mc and Mc+) One of the variation of M allele is Mc and Mc+. Although just one copy of Mc is not long enough to make visible change on coats, the combination of Mc or more than two copies of Mc would lead to odd shade of black/liver. * Atypical merle (Ma and Ma+) Another type of variation of M allele is Ma and Ma+. This kinds of allele would lead to visibly merle-patterned dog if there are two copies of Ma. It is important to be supplement because if the dog with atypical merle bred to dog with any longer merle allele, the double merle health problems might occur.S (spotting) locus
The alleles at the S locus (the microphthalmia-associated transcription factor gene or ''MITF'') determine the degree and distribution of white spotting on an animal's coat. There is disagreement as to the number of alleles that occur at the S locus, with researchers sometimes postulating a conservative two or, commonly, four alleles. The alleles postulated are: * ''S'' = Solid color/no white (very small areas of white may still appear; a diamond or medallion on the chest, a few toe tips/toes, or a tail tip) * ''si'' = Irish-spotting (white on muzzle, forehead, feet, legs, chest, neck and tail) * ''sp'' = Piebald (varies from coloured with Irish spotting plus at least one white marking on the top or sides of the body or hips, to mostly white which generally retains patches of colour around the eyes, ears and tail base) * ''sw'' = Extreme piebald spotting (extremely large areas of white, almost completely white) In 2014, a study found that a combination of simple repeat polymorphism in the MITF-M Promoter and a SINE insertion is a key regulator of white spotting and that white color had been selected for by humans to differentiate dogs from their wild counterparts. Based on this research the degree of White Spotting is dependent on the Promoter Length (Lp) to produce less or more color. A shorter Lp creates less white (Solid Colored and Residual White dogs) while a longer Lp creates more white (Irish Spotting and Piebald). What separates Piebald from Irish White and Solid is the presence of a SINE insertion (Short Interspersed Element) in the S locus genes that changes the normal DNA production. The result is Piebald and Extreme Piebald. The only difference between the two recognized forms of Piebald is the length of the Lp. Because of this variability, a dog's Phenotype will not always match their Genotype. The Beagle for example is fixed for ''spsp'' Piebald, yet there are Beagles with very little white on them, or Beagles that are mostly white. What makes them Piebald is the SINE Insertion, but the Lp length is what changes how their patterns are expressed. * White spotting can cause blue eyes, microphthalmia, blindness and deafness; however, because pigmentation is generally retained around the eye/ear area, this is rare except in SINE White dogs (Piebald) which can sometimes lose pigment in those areas during fetal development. * Some breeds like theAlbinism
C (colored) locus
People have postulated several alleles at the C locus and suggested some/all determine the degree to which an animal expresses phaeomelanin, a red-brown protein related to the production ofTheoretical genes for color and pattern
There are additional theoretical loci thought to be associated with coat color in dogs. DNA studies are yet to confirm the existence of these genes or alleles but their existence is theorised based on breeding data:F ( flecking) locus
The alleles at the theoretical F locus are thought to determine whether an animal displays small, isolated regions of white in otherwise pigmented regions (not apparent on white animals). Two alleles are theorised to occur at the ''F'' locus: * ''F'' = Flecked * ''f'' = Not flecked (See ticking below, which may be another name for the flecking described here) It is thought that ''F'' is dominant to ''f''.G (progressive greying) locus
The alleles at the theoretical G locus are thought to determine if progressive greying of the animal's coat will occur. Two alleles are theorised to occur at the G locus: * ''G'' = Progressive greying (melanin lost from hairs over time) * ''g'' = No progressive greying It is thought that ''G'' is dominant to ''g''. * The greying gene affects both eumelanin, and to a lesser extent phaeomelanin. In the presence of ''Em/-'' the eumelanin mask will be unaffected and remain dark. Grey dogs are born fully coloured and develop the greying effect over several months. New hairs are grown fully coloured but their colour fades over time towards white. Greying is most evident in continuous-growing coats (long + wire + curly) as individual hairs remain on the dog long enough for the colour to be lost. In short-haired dogs, hairs are shed out and re-grown before the colour has a chance to change. * Premature greying, in which the face/etc. greys at a young age is not caused by ''G'' and has not been proven to be genetic.T (ticking) locus
The alleles at the theoretical T locus are thought to determine whether an animal displays small, isolated regions of pigment in otherwise ''s''-spotted white regions. Two alleles are theorised to occur at the T locus: * ''T'' = Ticked * ''t'' = Not ticked It is thought that ''T'' is dominant to ''t''. Ticking may be caused by several genes rather than just one. Patterns of medium-sized individual spots, smaller individual spots, and tiny spots that completely cover all white areas leaving a roan-like or merle-like appearance (reserving the term large spots for the variation exclusive to the Dalmatian) can each occur separately or in any combination. * The effect of the ticking is to add back little coloured spots to areas made white by piebald spotting (''-/s'') or the limited white markings of ''S/S'' animals. It does not affect white areas that were caused by ''a/a e/e'' or ''M/M'' or ''M/m H/h''. The colour of the tick marks will be as expected or one shade darker. Tick marks are semi-random, so that they vary from one dog to the next and can overlap, but are generally present on the lower legs and heavily present on the nose.U (urajiro) locus
The alleles at the theoretical U locus are thought to limit phaeomelanin production on the cheeks and underside. Two alleles are theorized to occur at the U locus: * ''U'' = Urajiro * ''u'' = Not urajiro It is thought that ''U'' is recessive to ''u'' but due to lack of genetic studies these assumptions have only been made through visual assessment. The urajiro pattern is expressed in the tan (phaeomelanin) areas of any dog and does not effect black (eumelanin) pigment.Miscolours in dog breeds
Miscolours occur quite rarely in dog breeds, because genetic carriers of the recessive alleles causing fur colours that don't correspond to the breed standard are very rare in the gene pool of a breed and there is an extremely low probability that one carrier will be mated with another. In case two carriers have offspring, according to the law of segregation an average of 25% of the puppies are homozygous and express the off-colour in the phenotype, 50% become carriers and 25% are homozygous for the standard colour. Usually off-coloured individuals are excluded from breeding, but that doesn't stop the inheritance of the recessive allele from carriers mated with standard-coloured dogs to new carriers. In the breed Boxer large white markings in heterozygous carriers with genotype S si or S sw belong to the standard colours, therefore extreme white Boxers are born regularly, some of them with health problems. The cream-white colour of theGenes associated with hair length, growth and texture
Every hair in the dog coat grows from a hair follicle, which has a three phase cycle, as in most other mammals. These phases are: * ''anagen'', growth of normal hair; * ''catagen'', growth slows, and hair shaft thins; and * ''telogen'', hair growth stops, the follicle rests, and the old hair falls off—is shed. At the end of the telogen phase, the follicle begins the cycle again. Most dogs have a double coat, each hair follicle containing 1-2 primary hairs and several secondary hairs. The primary hairs are longer, thicker and stiffer, and called guard hairs or outer coat. Each follicle also holds a variety of silky- to wiry-textured secondary hairs (undercoat) all of which are wavy, and smaller and softer than the primary hair. The ratio of primary to secondary hairs varies at least six-fold, and varies between dogs according to coat type, and on the same dog in accordance with seasonal and other hormonal influences. Puppies are born with a single coat, with more hair follicles per unit area, but each hair follicle contains only a single hair of fine, silky texture. Development of the adult coat begins around 3 months of age, and is completed around 12 months. Research indicates that the majority of variation in coat growth pattern, length and curl can be attributed to mutations in four genes, the R-spondin-2 gene or RSPO2, the fibroblast growth factor-5 gene or FGF5, the keratin-71 gene or KRT71 and the melanocortin 5 receptor gene (MC5R). The wild-type coat in dogs is short, double and straight.L (length) locus
The alleles at the L locus (the fibroblast growth factor-5 gene or ''FGF5'') determine the length of the animal's coat. There are two known alleles that occur at the L locus: * ''L'' = Short coat * ''l'' = Long coat ''L'' is dominant to ''l''. A long coat is demonstrated when a dog has pair of recessive ''l'' alleles at this locus. The dominance of ''L > l'' is incomplete, and ''L/l'' dogs have a small but noticeable increase in length and finer texture than closely related ''L/L'' individuals. However, between breeds there is significant overlap between the shortest ''L/L'' and the longest ''L/l'' phenotypes. In certain breeds ( German Shepherd,W (wired) locus
The alleles at the W locus (the R-spondin-2 gene or ''RSPO2'') determine the coarseness and the presence of "facial furnishings" (e.g. beard, moustache, eyebrows). There are two known alleles that occur at the W locus: * ''W'' = Wire (hair is coarse and facial furnishings present) * ''w'' = Non-wire (hair is not coarse and facial furnishings are not present) ''W'' is dominant to ''w'', but the dominance of ''W > w'' is incomplete. ''W/W'' dogs have coarse hair, prominent furnishings and greatly-reduced shedding. ''W/w'' dogs have the harsh wire texture, but decreased furnishings, and overall coat length and shedding similar to non-wire animals. Animals that are homozygous for long coat (i.e., ''l/l'') and possess at least one copy of ''W'' will have long, soft coats with furnishings, rather than wirey coats.R (curl) locus
The ''R'' (curl) LocusResearchers have not yet assigned a letter to this locus and "R" has been selected based on the use of the term "Rex" for curled hair in domestic cats. The alleles at the R locus (the keratin-71 gene or ''KRT71'') determine whether an animal's coat is straight or curly. There are two known alleles that occur at the R locus: * ''R'' = Straight * ''r'' = Curly The relationship of ''R'' to ''r'' is one of no dominance. Heterozygotes (''R/r'') have wavy hair that is easily distinguishable from either homozygote. Wavy hair is considered desirable in several breeds, but because it is heterozygous, these breeds do not breed true for coat type. Corded coats, like those of the Puli and Komondor are thought to be the result of continuously growing curly coats (long + wire + curly) with double coats, though the genetic code of corded dogs has not yet been studied. Corded coats will form naturally, but can be messy and uneven if not "groomed to cord" while the puppy's coat is lengthening.Interaction of length and texture genes
These three genes responsible for the length and texture of an animal's coat interact to produce eight different (homozygous)Breed exceptions to coat type
Breeds in which coat type Is not explained by FgF5, RSPO2 and KRT71 genes: * Yorkshire Terrier, Silky Terrier *Other related genes
Hairlessness gene
Some breeds of dog do not grow hair on parts of their bodies and may be referred to as hairless. Examples of hairless dogs are theRidgeback
Some breeds (e.g.,Long Hair
There are many genes and alleles that cause long hair in dogs, but most of these genes are recessive. This means that longhaired hybrid breeds usually have to have two longhair or longhair carrier parents, and the gene can also be passed on for many generations without being expressed.Wire Hair
There are lots of variations of allele that would affect the dog's hair. The allele that causes bristles is actually dominant. Dogs with both the longhair and line coat genes will be "coarse," which means longer line coats of fur. Examples of such coats include the Korthals Griffon, and possibly the Irish Wolfhound.Nose colours
The most common colour of dog nose is black. However, a number of genes can affect nose colour. *A blue dog nose is genetically impossible. But greyhounds without the blue dilution gene are sometimes found. Therefore, a dog that appears to be "blue" may have a black nose and black eyes because it is actually a black dog with the gray gene, not a proper blue diluent. Sometimes the blues can also be so dark that their coats and noses look almost black. It's hard to tell if these dogs are black or blue. *A "butterfly" nose is a bright pink patch lacking pigment on the skin of a dog's nose. The patches are randomly positioned and can cover any number of noses, from a tiny pink blob to almost the entire nose. Butterfly noses are sometimes seen on dogs with extreme white spotted patterns, but usually they are associated with meteorite coloration. The meteorite gene diluted the random portion of pigment in the hair and nose, forming gray areas in the hair and pink areas in the nose. Liver and Isabella's nose are usually very light, sometimes completely pink or bright pink, so the butterfly nose may not appear in the liver or Isabella meteorite color. *"Dudley nose" is a dog with a loss of pigment on its nose. Typically, the pigment loss on Dali's nose is in the middle and spreads outward, covering almost the entire nose of some dogs. Dudley's nose will never completely lose its pigment, nor will it be as bright pink as a butterfly's or even a liver dog's. Dudley noses are common in blacknosed dogs and are particularly associated with the recessive red gene.Eye Colours
The genes also affect the eye colours of dogs. There are two main types of eye colours patterns.Amber eyes
All hepatic dogs (bb) have amber eyes. Amber eyes vary from light brown to yellow, chartreuse, or gray. Dogs with melanin can occasionally see amber eyes. rticle refers to Dr Sheila M. Schmutzref name="auto2">Blue eyes
Blue eyes in dogs are often related to pigment loss in coatings. *The merle gene results in a bluish iris, and merle dogs often have blue, walled, or split eyes due to random pigment loss. Some genetic variants causeGenetic testing and phenotype prediction
In recent years genetic testing for the alleles of some genes has become available. Software is also available to assist breeders in determining the likely outcome of matings.Characteristics linked to coat colour
The genes responsible for the determination of coat colour also affect other melanin-dependent development, including skin colour, eye colour, eyesight, eye formation and hearing. In most cases, eye colour is directly related to coat colour, but blue eyes in the Siberian Husky and related breeds, and copper eyes in some herding dogs are not known to be related to coat colour. The development of coat colour, skin colour, iris colour, pigmentation in back of eye and melanin-containing cellular elements of the auditory system occur independently, as does development of each element on the left vs right side of the animal. This means that in semi-random genes (''M'' merle, ''s'' spotting and ''T'' ticking), the expression of each element is independent. For example, skin spots on a piebald-spotted dog will not match up with the spots in the dog's coat; and a merle dog with one blue eye can just as likely have better eyesight in its blue eye than in its brown eye.Loci for coat colour, type and length
All known genes are on separate chromosomes, and therefore noSee also
* Labrador Retriever coat colour genetics * Cat coat genetics * Equine coat color genetics * Farm-Fox Experiment *Notes
References
External links
*{{cite web , last = Schmutz , first = Sheila M. , title = Dog Coat Color Genetics , publisher = Sheila Schmutz , date = March 4, 2010 , url = http://munster.sasktelwebsite.net/DogColor/dogcolorgenetics.html , access-date = July 24, 2020 Dog anatomy Animal hair Animal coat colors