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Coat color in dog

Eumelanin and phaeomelanin pigments

The basic color of the dogs is determined by only two basic pigments eumelanin and phaeomelanin. Eumelanin is responsible for the black, brown, chocolate, gray and taupe pigments. Phaeomelanin is responsible for the tan pigment, all shades of red, cream and gold pigment. The lack of Eumelanin and Phaeomelanin induce a white coat color.

The production and quantity produced of these two pigments,and thus the coat color of the dog, are determined by numerous genes (around 14 genes). However, the basic color of the dog’s coat is determined by the interactions 3 genes, which are called : E locus, K locus and A locus. The interactions between these 3 genes are presented in the table below.

Others genes play a key role by modifying the basic coat color of the dog. These genes can either darken the dog’s coat or lighten the dogs’s coat or they can also result in color patterns on the dog’s coat.

E, k, A locus

The A locus for Agouti affect both eumelanin and phaeomelanin pigments. The A locus is not expressed if K locus has the dominant black allele (K/K, K/k, K/kbr). Six alleles are recognized :
  • the Ay for the Fawn or sable. Y stands for yellow.
  • the aw which is the wild type allele. It is also called wolf sable. Each hair had 6 bands alternating tan and black.
  • the at which is the black and tan coat color
  • the a which is the recessive black due to no production of phaeomelanin
  • the ayt allele is called recombinant fawn and has been observed in Tibetan Spaniels and a Tibetan Mastiff.
Four alleles can be tested at Genimal Biotechnologies : the Ay, the aw, the at, and the a with the agouti DNA test. The hierarchical order of the agouti alleles are Ay > aw > at > a. More details on the E locus can be found in the section below specific to this locus. The K locus has 3 alleles :
  • K which is the dominant black. The A locus has no effect on dominant black. However there is an effect of B, D and M loci.
  • kbr which is responsible for the brindle coat color. Brindle color is due to the presence of eumelanin stripes to all tan areas. The intensity of the brindle is influenced by the A locus.
  • ky is the wild types and all other loci can be expressed with this allele.
The K and ky can be tested here, whereas the kbr allele can be tested here. The kbr test includes also the detection of the K and ky alleles.

E locus

e/e

Recessive red

No effect of K and A locus

E/e, E/E or Em Eg Eh alleles

K locus

k/k

A locus

See the A chart below

K/K, K/k, K/kbr

Dominant black

No effect of A locus. Effect of M, B, D locus

kbr/kbr, kbr/k

Brindle

Extend of brindle depends on A locus

Locus A

Ay/aw, Ay/at, Ay/a

Fawn or sable

aw/aw, aw/at, aw/a

Wolf grey (agouti)

at/at, at/a

Black and tan or tricolor

a/a

Recessive black

E locus and mask on the dog’s head

The E locus determine the mask of the dog and whether eumelanin can be produce and thus present in the dog’s coat. Five alleles are recognized:
  • Em which is the melanistic mask. The mask is not present in dominant black dog and in recessive black dog. The mask is present in sable or fawn, black and tan, and wolf gray (agouti) coat color. Depending of the breed, the mask can cover the chest and legs.
  • EG which result in grizzle or domino coat color. This coat color is found in Saluki, Afghan Hound and Barzoi.
  • E which is the normal extension and allow the full expression of A and K loci.
  • eh which the cocker sable and is found in cocker spaniel only.
  • e which is the recessive or clear fawn.
The hierarchical dominance of these loci is a follow Em > EG > E > eh > e. The alleles E, Em and e can be tested here.

E locus

e/e

Recessive red

No effect of K and A locus

E/E, E/e

No effect of E

Effect of K and A locus

Em/Em, Em/E, Em/e

Melanistic mask

Can be hidden by others colors

Eg/e, Eh/E, Eh/e

Sable (Cocker)

Cocker Spaniel only

Eg/Eg, Eg/E, Eg/e

Grizzle/Domino

Need Tan on locus A

The genes that change the basic color of the dog's coat

There are 6 other genes that alter the basic color of the dog’s coat.

B locus

The B locus affects mainly eumelanin only and is reponsible of brown or liver coat color. The phaeomelanin pigment is slightly reduced from red to orange tan. Different alleles are recognized and generally 2 or 3 alleles are presents per breed. Only one of the alleles is present in the English Setter (bs), in the Doberman Pinscher (bd) and in the Italian Greyhound (bc). A DNA test exists for the B locus and can be ordered here.

Basic coat color

Locus E, K, A

B/B, B/b

Non Brown

b/b

Brown

D locus

The locus D is responsible of the dilution of both pigments eumelanin and phaeomelanin. The black coat color is diluted in blue and the brown coat color becomes isabella. A DNA test exists for this locus and can be ordered here. The genotype d/d is sometimes responsible of hair loss (BHFD) and skin inflammation (CDA) in some breeds.

Basic coat color

Locus E, K, A

D/D, D/d

Non Dilute

d/d

Dilute

S locus

The locus S is the result of spotting. Four alleles are recognized :
  • S which is a non spotting dog. However some small white area can appear in the coat often in the tail or the toes.
  • si is called the Irish spotting.
  • sp is called Piebald. The amount of spotting varies greatly according to the breed and to each dog.
  • sw is called the extreme piebald spotting. This coat is nearly all white.
To date, all the allele of the S locus can not been tested by a DNA test.

Basic coat color

Locus E, K, A

S/S

No white spotting

S/sp, sp/sp

White spotting

M and H locus

The M locus is responsible of the Merle coat color (similar to silver color). The Merle locus has a particular dominance:
  • M/m genotype is responsible of 50% of the black which is transformed into silver.
  • M/M genotype is called double merle and black is replace by around 25% of black, around 50% of silver and around 25% of white.
The DNA test of Merle can be ordered here. The H locus is named Harlequin and is specific to Great danes. No DNA test exist for this locus. The locus H is only expressed when the dog is M/m in the M locus.

Basic coat color

Locus E, K, A

M locus

H locus

M/m H/h

Merle Harlequin

M/m h/h

Merle, Non Harlequin

m/m H/h

Non merle non harlequin

m/m h/h

Non merle non harlequin

Other theoretical genes that affect dog's coat color

There are also 6 other genes that exist theorically. The breeding data proves the existence of this gene even if today that mutations have not been identified.

I locus (Intensity)

Locus I influence the intensity of the dog coat color by affecting the phaeomelanin production. Two alleles exists (I and i). This gene is now identify and you can test your dog for the I locus here.

C locus (colored)

The C locus is probably responsible of the degree to which an animal expresses phaeomelanin. Five alleles are theorised :
  • C which is the full color
  • cch for Chinchilla
  • ce which is an extreme dilution
  • cb, cp which are Blue-eyed albino and Platinum
  • ca which is albino. However true albino in dog has not been proved.
Today no colortest C exist in the dog.

F locus (Flecking)

Locus Flecking is reponsible of isolated and small area of white in the coat color. However the gene involved has not been identified.

G locus (progressive greying)

G locus is responsible of a progressive greying of the coat color with the age. The grey allele is dominant. No DNA test exists.

T locus (Ticking)

The T locus is responsible of small pigment region. No DNA test currently exists.

U locus (Urajiro)

The U locus reduced the phaeomelanin production on the cheeks and underside. The gene involved has not been currently discovered.
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