Coat (dog)



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.

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 in to 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 (cream to red hair with darker tips) or sable (solid black hairs interspersed amongst lighter reddish hairs)
 * As = Saddling
 * at = Tan points; Tricolors
 * a = Recessive black (inhibition of phaeomelanin)

Most texts suggest that the dominance hierarchy for the A locus alleles appears to be as follows: Ay > As > 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 As may be incompletely dominant over at.

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:


 * E = No 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)
 * Em = Mask, animal expresses eumelanin (coat will be black or brown)
 * 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 > e. The Grizzle allele is specific to Salukis and Afghan Hounds, the latter in which it is referred to as "Domino". The expression of EG is dependant 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

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 = 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 intese 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

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.

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 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

R is dominant to r.

Interaction of Length & Texture Genes

These three genes responsible for the length and texture of an animal's coat interact to produce seven different phenotypes:


 * 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)

Hair growth


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. Examples of breeds of dog whose coats grow continuously are:
 * Australian Silky Terrier
 * Bedlington Terrier
 * Bichon Frisé
 * Irish Water Spaniel
 * Kerry Blue Terrier
 * Maltese
 * Poodle
 * Portuguese Water Dog
 * Schnauzer
 * Skye Terrier
 * Soft Coated Wheaten Terrier
 * Yorkshire Terrier

Corded Coats

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.

Hairless

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 one or more dominant alleles, one or more of which is homozygous lethal.

Genetic 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.

Colors
The same color may be referred to differently in different breeds.

Patterns
The same pattern may be referred to differently in different breeds.

Show coats
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.

Shedding


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.

Many dogs shed their undercoat each spring and regrow it again as colder weather comes in; this is also referred to as blowing the coat. Many domesticated breeds shed their coat twice a year. In some climates, the topcoat and undercoat might shed continuously in greater and smaller quantities all year.

Hypoallergenic coats


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, yorkies, and terriers (and mixes of poodles 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..."