The coat of the domestic dog (Canis lupus familiaris) refers to the hair that covers its body. A dog's coat may be a double coat, made up of a soft undercoat and a coarser topcoat, or a single coat, which lacks an undercoat. The terms fur and hair are often used interchangeably when describing a dog's coat, however in general, a double coat, e.g., like that of the Newfoundland and most mountain dogs, is referred to as a fur coat, while a single coat, like that of the Poodle, is referred to as a hair coat.
- 1 Colors, patterns, lengths and textures
- 2 Nomenclature of colors and patterns
- 3 Show coats
- 4 Shedding
- 5 Hypoallergenic coats
- 6 See also
- 7 Notes
- 8 References
- 9 Additional reading
- 10 External links
Colors, patterns, lengths and textures
There are a greater variety of coat colors, patterns, lengths and textures found in the domestic dog than in its wolf relations, even though dogs and wolves belong to the same species (Canis lupus). Different breeds use different names for longhaired and shorthaired types, there is no standard nomenclature for length, breed standards give acceptable lengths by measurement. Coat colors in dogs were not likely initially selected for by humans but were probably the inadvertent outcome of some other selection process (i.e. selection for tameness). Research has found that tameness brings associated physical changes, including coat coloring and patterning.
Domestic dogs often display the remnants of countershading, a common natural camouflage pattern. The basic principle of countershading is when the animal is lit from above, shadows will be cast on the ventral side of the body. These shadows could provide a predator or prey with visual cues relating to the movement of the animal. By being lighter colored on the ventral side of the body, an animal can counteract this, and thereby fool the predator or prey. An alternative explanation is that the dorsal and ventral sides of an animal experience different selection pressures (from the need to blend into different backgrounds when viewed from above and below) resulting in differing coloration.
Genetic basis of color and pattern
Modern breeds of dog exhibit a diverse range of coat colorings, patterns, lengths and textures. In recent years, the understanding of the genetic basis for coat coloring and patterning and coat length and texturing has increased significantly.
There are currently eight known genes within the canine genome that are associated with coat color. Each of these genes occurs in at least two variants, or alleles, which accounts for the variation in coat color between animals. Each of these genes exists at a fixed location, or locus, of the animal's genome. The loci associated with canine coat color are:
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 if so what type, by controlling the distribution of pigment in individual hairs. There are five suspected alleles that occur at the A locus:
- aw = Wild-type agouti (cream to red hair with black tips)
- Ay = Fawn/clear sable (cream to red hair with darker tips) or sable (solid black hairs interspersed amongst lighter reddish hairs)
- at = Tanpoint including saddle tan,
- a = Recessive black (inhibition of phaeomelanin)
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/recessive relationships in different families and not the existence of a single hierarchy in one family. This means, for example, that Ay may be incompletely dominant over at. Recent studies reveal saddle tan to be a modification of the tanpoint phenotype caused by interaction of other genes with ASIP.
B (brown) locus
The alleles at the B locus are related to the production of tyrosinase related protein 1 (TYRP1) and determine the degree to which an animal expresses tyrosinase, an enzyme related to the production of melanin, in its coat and skin (including the nose and paw pads). There are two known alleles that can occur at the B locus:
- B = Black
- b = Brown (includes several alleles - bs, bd and bc)
B is dominant to b. An animal that has at least one copy of the B allele will have a black nose, paw pads and eye rims while an animal that is homozygous for any of the b alleles will have a liver nose, paw pads and eye rims.
D (dilute) locus
The alleles at the D locus (the melanophilin gene or MLPH) are related to the dilution of eumelanin and/or phaeomelanin and determine the intensity of pigmentation. There are two known alleles:
- D = Not Diluted
- d = Diluted (Black becomes grey or blue; brown becomes light tan or "Isabella")
D is dominant to d. Homozygosity of d is sometimes accompanied by hair loss and recurrent skin inflammation, a condition referred to as either color dilution alopecia (CDA) or black hair follicular dysplasia (BHFD) depending upon the breed of dog.
E (extension) locus
The alleles at the E locus (the melanocortin receptor 1 gene or MC1R) determines whether an animal expresses a melanistic mask or a grizzle overlay, as well as determining whether an animal expresses eumelanin in its coat. Expression of eumelanin will result in a black or brown coat, while a lack of expression of eumelanin will result in a red or yellow coat. There are four known alleles that occur at the E locus:
- Em = Mask, animal expresses eumelanin (coat will be black or brown)
- EG = Grizzle (dark overlay covering the top and sides of the body, head and tail, and the outside of the limbs)
- E = No mask, animal expresses eumelanin (coat will be black or brown)
- eh = Sable - dirty red, found in English Cocker Spaniels (dark overlay covering the top and sides of the body, head and tail, and the outside of the limbs)
- e = No mask, animal does not express eumelanin (coat will be red or yellow)
The dominance hierarchy for the E locus alleles appears to be as follows: Em > EG > E > eh > e. The Grizzle allele has been studied only in Salukis and Afghan Hounds, the latter in which it is referred to as "Domino". Its placement in the dominance hierarchy has not been solidified. The eh sable extension allele has been studied only in English Cocker Spaniels and produces sable in the presence of all K locus alleles. The expression is dependent upon the animal being homozygous for at and not possessing Em or E. The expression of EG is dependent upon the animal being homozygous for at and not possessing Em or KB. An animal that is homozygous for e will express a red or yellow coat regardless of the alleles at other loci (unless the animal is homozygous for ca at the C locus in which case it will be albino).
H (harlequin) locus
DNA studies have not yet isolated the gene at the H locus, but the traits associated with it have been mapped to chromosome 9. 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 pattern (white base with black patches). There are two alleles that can occur at the H locus:
- H = Harlequin
- h = Non-harlequin
H is dominant to h. Breeding data suggests that H is embryonic recessive lethal and that therefore all harlequins are H/h. The Harlequin allele is specific to Great Danes. As H is a modifier locus of the M locus, in order for the Harlequin pattern to be expressed, one copy of the H allele (at the H locus) and one copy of the M allele (at the M locus) must be present (i.e. H/h and M/m).
K (dominant black) locus
- KB = Solid coloring (does not mean that white markings can not appear)
- kbr = Brindle
- ky = Enables the expression of agouti alleles that require the expression of phaeomelanin
The dominance hierarchy for the K locus alleles appears to be as follows: KB > kbr > ky. The coloring of an animal that possesses at least one KB will be determined by the alleles it possesses at the B and E loci. An animal with one kbr allele and no KB allele will express a brindle pattern to its coat unless it is homozygous for e (at the E locus) or possibly homozygous for a (at the A locus). An animal that is homozygous for ky will express the agouti pattern in accordance with the alleles it has at the A locus.
M (merle) locus
The alleles at the M locus (the SILV gene) determine whether an animal expresses a merle pattern to its coat (patches of sporadic colored and white hairs and other patches of solid color). There are two alleles that can occur at the M locus:
- M = Merle (visible in dogs that are not e/e)
- m = Non-merle
M is dominant to m. Both heterozygosity and homozygosity of the merle gene (i.e. M/m and M/M) are linked to a range of auditory and ophthalmologic abnormalities.
S (spotting) locus
The alleles at the S locus (the microphthalmia-associated transcription factor gene or MITF) determine the degree and distribution of spotting of an animal's coat. There is disagreement as to the number of alleles that occur at the S locus, with researchers postulating either two or four alleles. The four alleles postulated are:
- S = Solid color (small areas of white may appear on chest, toes or tail tip)
- si = Irish-spotting (white on muzzle, forehead, feet, legs, chest and tail)
- sp = Pie-bald spotting (large areas of white)
- sw = Extreme pie-bald spotting (Extremely large areas of white, almost completely white)
S is dominant to s. DNA studies have not yet confirmed the existence of all four alleles, with some research suggesting the existence of at least two alleles (S and sp) and other research suggesting the possible existence of a third allele (si). It has been suggested that what appears to be the result of an sw allele is in fact the result of plus and minus modifiers acting on one of the other alleles. It is thought that the spotting that occurs in Dalmatians is the result of the interaction of three loci (the S locus, the T locus and F locus) giving them a unique spotting pattern not found in any other breed.
Postulated color and pattern loci
There are at least five 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:
C (colored) locus
The alleles at the theoretical C locus are thought to determine the degree to which an animal expresses phaeomelanin, a red-brown protein related to the production of melanin, in its coat and skin. Five alleles are theorised to occur at the C locus:
- C = Full color (animal expresses phaeomelanin)
- cch = Chinchilla (partial inhibition of phaeomelanin resulting in decreased red pigment)
- ce = Extreme dilution (inhibition of phaeomelanin resulting in extremely reduced red pigment)
- cb/cp = Blue-eyed albino/Platinum (almost total inhibition of phaeomelanin resulting in near albino appearance)
- ca = Albino (complete inhibition of phaeomelanin production, resulting in complete inhibition of melanin production)
The C locus in dogs is not well understood and the theorised alleles are based on those present in other species. True albinism has not been conclusively shown to exist in dogs. It is thought that an animal that is heterozygous for the C allele with one of the other alleles will express a result somewhere between the two alleles.
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: they cAN BE PINK
- F = Flecked
- f = Not flecked
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 premature greying of the animal's coat will occur. Two alleles are theorised to occur at the G locus:
- G = Premature greying
- g = No premature greying
It is thought that G is dominant to g.
I (intensity) locus
The alleles at the theoretical I locus are thought to affect phaeomelanin expression. Two alleles are theorised to occur at the I locus:
- I = Intense red, not diluted
- i = Not intense red
It is thought that I and i are co-dominant, so that animals with i/i will be paler than animals with I/i.
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 white regions (not apparent on non-white animals). Two alleles are theorised to occur at the T locus:
- T = Ticked
- t = Not ticked
It is thought that T is dominant to t.
Genetic basis of length and texture
Research indicates that the majority of variation in coat growth pattern, length and curl can be attributed to mutations in three genes, the R-spondin-2 gene or RSPO2, the fibroblast growth factor-5 gene or FGF5, and the keratin-71 gene or KRT71.
The L (length) 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 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. Animals that are homozygous for l (i.e. l/l) and possess at least one copy of W will have long, soft coats with furnishings, rather than wirey coats.
The R (curl) Locus[note 1]
- R = Straight
- r = Curly
R is dominant to r.
Interaction of Length & Texture Genes
- Short (e.g. Basset Hound)
- Wire (e.g. Australian Terrier)
- Curly-wire (e.g. Airedale Terrier)
- Long (e.g. Golden Retriever)
- Long with furnishings (e.g. Bearded Collie)
- Long and curly (e.g. Irish Water Spaniel)
- Long and curly with furnishings (e.g. Bichon Frisé)
The coat of most dogs grows to a specific length and then stops growing, while the coats of some dogs grow continuously in a manner similar to human hair growth. A long coated dog with a single dominant furnishings allele (wire coat), will demonstrate this feature. Examples of breeds of dog whose coats grow continuously are:
- Australian Silky Terrier
- Bedlington Terrier
- Bichon Frisé
- Skye Terrier
- Soft Coated Wheaten Terrier
- Yorkshire Terrier
- Shih Tzu
- Lhasa Apso
- Coton de tulear
- Tibetan terrier
Corded coats, like those of the Puli and Komondor are thought to be the result of continuously growing curly coats. Other breeds with continuously growing curly coats, such as the Poodle, can also be groomed to cord.
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 the Xoloitzcuintli (Mexican Hairless Dog), the Peruvian Inca Orchid (Peruvian Hairless Dog) and the Chinese Crested. Research suggests that hairlessness is caused by a dominant allele, which is homozygous lethal.
Genetic testing and phenotype prediction
Nomenclature of colors and patterns
The same color may be referred to differently in different breeds.
Brown Chesapeake Bay Retriever
Dark chocolate Australian Kelpie
|Brown and its variants, including mahogany, midtone brown, grey-brown, blackish brown; the Chesapeake Bay Retriever, whose color "must be as nearly that of its working surroundings as possible", also uses the terms sedge and deadgrass. Also includes liver or chocolate, a dark brown.|
Red Irish Setter
Red Chow Chow
|Red—reminiscent of reddish woods such as cherry or mahogany—and its variants, including chestnut, tawny, orange, roan, rust, red-gold, reddish brown, bronze, cinnamon, tan, and ruby.|
Dark Golden Retriever
|Gold Rich reddish-yellow, as in a Golden Retriever, and its variants, including yellow-gold, lion-colored, fawn, apricot, wheaten (pale yellow or fawn, like the color of ripe wheat), tawny, straw, yellow-red, mustard, sandy, honey.|
Yellow Labrador Retriever
|Yellow—yellowish-gold tan, as in a yellow Labrador Retriever—and its variants, including blond and lemon. Lemon is a very pale yellow or wheaten color which is not present at birth (the puppies are born white) but gradually becomes apparent, usually during the first six months of life.|
Cream French Bulldog
|Cream: Sometimes it's hard to define the line between pale yellow and cream. Depending on the breed and individual, cream ranges from white through ivory and blond, often occurring with or beneath lemon, yellow, and sable.|
Black Labrador Retriever
|Black: Usually pure black but sometimes grizzled, particularly as dogs age and develop white hairs, usually around the muzzle.|
Progressive grey ("blue") Kerry Blue Terrier
Blue mixed-breed dog
|Blue: A dark metallic grey, often as a blue merle, speckled with black. Kerry Blue Terriers, Australian Silky Terriers, Australian Shepherds, Bearded Collies, Great Danes, and Neapolitan Mastiffs are among the many breeds that come in colourations named "blue".|
Lilac grey Weimaraner
Salt and pepper grey Miniature Schnauzer
|Grey—sometimes also called blue—and its variants, including pale to dark grey, silver, pepper, grizzle, slate, blue-black grey, black and silver, steel, lavender, silver-fawn.|
White American Eskimo Dog
White Bichon Frisé
|White: Such a light cream that it is seen and described as pure white, making them distinct from albino dogs. A white dog, as opposed to an albino one, has dark pigment around the eye rims and nose, often coupled with dark-colored eyes. There is often some coat identifiable as cream between the dog's shoulder blades.|
The same pattern may be referred to differently in different breeds.
Liver and tan Australian Kelpie
Black and tan Rottweiler
|Black and tan, liver and tan, blue and tan: Coat has both colors but in clearly defined and separated areas, usually with the darker color on most of the body and tan (reddish variants) underneath and in highlights such as the eyebrows. Black and brindle and liver and brindle, in which the same pattern is evident with brindling in place of tan, are also possible, but less common.|
Black and white Border Collie
Blenheim (Red-brown and white) Cavalier King Charles Spaniel
|Bicolor (also called Two-color, Irish spotted, Flashy, Patched, Tuxedo) Any color or pattern coupled with white spotting. This can range anywhere from white toes and tail tip to a mostly-white dog with color around the base of the ears and tail. Some breeds have special names for the color combinations; for example, Cavalier King Charles Spaniel uses Blenheim for reddish brown (chestnut) and white. Irish Spotted or flashy pattern is symmetrical and includes a white chest, white band around the neck, white belly, and white feet or "boots." This pattern is commonly seen in herding dogs, and Boxers, among others. The piebald gene is responsible for this pattern.|
Black tricolor Entlebucher Mountain Dog
|Tricolor: Three clearly defined colors, usually either black, liver, or blue on the dog's upper parts, white underneath, with a tan border between and tan highlights; for example, the Smooth Collie, the Rough Collie, the Papillon,or the Sheltie. Tricolor can also refer to a dog whose coat is patched, usually two colors (such as black and tan) on a white background.|
Blue merle tricolor Australian Shepherd
Red merle Catahoula Leopard Dogs
|Merle: Marbled coat with darker patches and spots of the specified color. Merle is referred to as "Dapple" with Dachshunds.|
Tuxedo mixed-breed dog.
|Tuxedo: Solid (often black) with a white patch (shirt front) on the chest and chin, and white on some or all of the feet (spats.) The tuxedo pattern is common in dogs that carry only one piebald gene (a heterozygous carrier).|
Harlequin Great Dane
Harlequin Great Dane
|Harlequin: "ripped" splotches of black on white. The Great Dane is the only breed with this pattern. Sometimes, like with the parti-colored poodle Poodle, the term 'harlequin is incorrectly used to describe the coat pattern, but the gene responsible for the patches of color in some poodles is piebald, which is present in many dog breeds and most of the ones which some white on their coats.|
Spotted mutt in Sinamaica, Venezuela
|Spotted Most often dark pigmented spots on a light background. The spotting on dalmatians is unique as it involves mutations in at least three different spotting genes.|
Red-speckled Australian Cattle Dog
Liver-ticked German Shorthaired Pointer
|Flecked, ticked, speckled: also called belton in English Setters|
Orange belton (orange and white speckled) English Setter
Blue speckled Australian Cattle Dog
Darker brindle and white Boston Terrier
Medium brindle Galgo Español
|Brindle: A mixture of black with brown, tan, or gold; usually in a "tiger stripe" pattern.|
Dark brindle Mountain Cur
Very sparsely brindled Great Dane
Airedale Terrier with large black saddle
Norwegian Dunker with merled black saddle
|Saddle or blanket: A different color, usually darker, over the centre of the back.|
Dark orange sable Pomeranian
Lighter sable Shetland Sheepdogs
|Sable: Black-tipped hairs; the background color can be gold to yellow, silver, grey, or tan. The darkness of the coat depends on how much of each hair is black versus the lighter color.|
The nature and quality of a purebred dog's coat is important to the dog fancy in the judging of the dog at conformation shows. The exact requirements are detailed in each breed's breed standard and do not generalise in any way, and the terminology may be very different even when referring to similar features. See individual breed articles for specific information.
Every hair in the dog coat grows from a hair follicle, which has a cycle of growing, then dying to be replaced by another follicle. When the follicle dies, the hair is shed (moults). The length of time of the growing and shedding cycle varies by breed, age, and by whether the dog is an inside or outside dog.
Some dog breeds have been promoted as hypoallergenic (which means less allergic, not free of allergens) because they shed very little. However, no canine is known to be completely nonallergenic. Often the problem is with the dog's saliva or dander, not the fur. Although poodles, bichons, yorkies, and terriers are commonly represented as being hypoallergenic, the reaction that an individual person has to an individual dog may vary greatly. In treating dog related allergies, it has been found that "Factors related to individual dogs seem to influence the allergenicity more than breed..."
- Cat coat genetics
- Dog grooming
- Equine coat color genetics
- Farm-Fox Experiment
- List of dog breeds
- Merle (coat color in dogs)
- Dog skin disorders
- Researchers 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.
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