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Genetics

The coat color genes in the French Bulldog panel are E, A, D, K & S There are a number of genes which

interact to dictate the coat color of a dog – the genes tested in this panel are the main ones which

dictate the coat color in French bulldogs. Colors which dogs carry are often hidden but become apparent

in their offspring. It is in identifying these hidden genes that genetic testing has value. Genetic testing

can be used to identify some of the genes that a dog carries, and to help identify the possible outcome

when dogs are bred. As with all genetic traits, every animal inherits one copy of each locus from each of

its parents. So, each gene test gives two results for each dog – one has come from his father and the

other his mother. These are usually written one after the other e.g., at at.
 

More details about each gene test below:

The E Gene

In dogs the production of the two pigments eumelanin (black) and pheomelanin (red/yellow/cream) is

controlled by the Melanocortin 1 Receptor (MC1R) gene, also known as Extension. The four alleles

(variants) of this gene are, in order of dominance: melanistic mask (E m ), grizzle (E g ), black (E) and red (e).

Some dog breeds are fixed for either black or red pigment, such as the Large Munsterlander for black

and Irish Setters for red.
 

Melanistic face mask is found in a variety of breeds including but not limited to Afghans, Akitas, Boxers,

French Bulldogs, German Shepherds, Great Danes, Greyhounds, Pug Dogs and Whippets. For Pug Dogs

and Boxers, the trait is fixed, while it is variable in other breeds. Dogs that are overall eumelanistic

(black, blue, or brown) may have the mask, but it is indistinguishable from the body color. Dogs with

white muzzles may have the mask gene but expression is overridden by white spotting patterns. The

mask phenotype is caused by the E m variant at the MC1R gene.

Grizzle (also called domino) is a pattern of dark pigment (eumelanin) on the dorsal surface of the head,

body, and tops of the legs; light pigment (pheomelanin) is present on the lower legs, undersides and up

the face around the eyes. The distinctive face pattern is often referred to as a widow’s peak. This variant

has been seen in Afghan, Borzoi, Chart Polski and Saluki hounds. Grizzle can only be expressed when the

Dominant black gene is not present (N/N), and the agouti gene is a t /a t .

This test screens for all 4 variants to provide a complete analysis and a better understanding of

phenotype and breeding expectations.

 

Results are reported as:

Em/Em 2 copies of mask- dog has mask

Em/Eg 1 copy of mask and 1 copy of grizzle- dog has mask and carries grizzle

Em/E 1 copy of mask and 1 copy of black- dog has mask and carries black

Em/e 1 copy of mask and 1 copy of red/yellow- dog has mask and carries red/yellow/cream

Eg/Eg 2 copies of grizzle-dog is grizzle if Dominant black is N/N and agouti is at/at

 

Eg/E 1 copy of grizzle and 1 copy of black- dog is grizzle if Dominant black is N/N and agouti is

 

at/at

 

Eg/e 1 copy of grizzle and 1 copy of red/yellow/cream-dog is grizzle if Dominant black is N/N

and agouti is at/at

 

E/E 2 copies of black

E/e 1 copy of black and 1 copy of red/yellow/cream

e/e 2 copies of red/yellow are present. Dog is red/yellow/cream

The A Gene

The Agouti Signaling Protein (ASIP) gene interacts with the MC1r gene to control red and black pigment

switching in most mammals including dogs. Dog coat color is further complicated by the interaction of

other genes that restrict agouti expression such as the dominant black gene – Beta-Defensin 103. There

are 4 known alleles (variants) of agouti listed here with corresponding color pattern in order of

dominance: fawn/ sable (ay) yellow to red with some dorsal black tipped hairs, wild sable (aw ) banded

hairs of yellow and black as in seen in wolves and coyotes, black and-tan (at ) black dorsal hairs with tan

hair on cheeks, eyebrows and undersides, and recessive black (a) all black as seen in some herding dogs.

The Eurasier dog breed has all 4 alleles while some breeds are fixed for only one variant such as the

Norwegian Elkhound for wild sable and the Beagle for black-and-tan. For many breeds, there are 2 or 3

alleles possible, and it may be advantageous for breeders to predict the possible colors of offspring

resulting from specific mating. The agouti test is also useful to help determine the color of dogs that

have white patterns that may obscure the distribution of the colored pigment.
 

This test will help determine possible coat color outcomes from specific mating.

 

Results are reported as:

a y / a y Homozygous for fawn/ sable.

a y / a w Dog is fawn and carries wild sable.

a y / a t Dog is fawn and carries black-and-tan.

a y / a Dog is fawn and carries recessive black.

a w / a w Homozygous for wild sable.

a w / a t Dog is wild-sable and carries black-and-tan.

a w / a Dog is wild-sable and carries recessive black.

a t / a t Homozygous for black-and-tan.

a t / a Dog is black-and-tan and carries recessive black.

a/a Homozygous for recessive black.

The D Gene

A recessive mutation in the melanophilin (MLPH) gene was identified as the cause of color dilution

phenotypes in the dog. Two alleles (variants) are described: the dominant full color (D) and the recessive

dilute (d). Two copies of dilute are needed to lighten black pigment to grey (often called blue) and red

pigment to cream (also called buff). A diagnostic DNA test identifies the specific variants of the MLPH

gene.

 

Results from the DILUTE test are reported as:

D/D Full color, no dilute gene present.

D/d Full color, carries 1 copy of the dilute gene.

d/d Dilute, 2 copies of the dilute gene.

The K Gene

The wide variety of coat colors in mammals is achieved by the production of two pigments, eumelanin

(black) and pheomelanin (red or yellow). In most mammals, the switching between these 2 pigments is

controlled by MC1R and Agouti genes. In dogs, original coat color research of pedigrees suggested that a

third gene, named Dominant Black (K locus), was involved. This gene produces dominant black vs.

brindle vs. fawn colors in breeds such as Great Danes, Pugs and Greyhounds among others. Researchers

recently have discovered that dominant black is due to a mutation in a Beta-defensin gene (CBD103).

This test can assist owners of black dogs to determine if their dogs are homozygous for dominant black

or if they carry brindle or fawn.

 

Results are reported as:

K/K 2 copies of dominant black are present.

K/N* 1 copy of dominant black is present.

N/N Dog does not have the dominant black mutation.

 

* This result is sometimes associated with the brindle pattern

The S Gene

White spotting patterns that occur in many dog breeds do not have a uniform genetic basis. Some white

patterns, such as the Irish spotting, are symmetrical with white markings on the undersides, collar, and

muzzle, and/or blaze such as seen in Boston Terriers and Corgis. The white pattern called mantle is

phenotypically like Irish spotting but with more white extending onto the thigh and up the torso, as seen

in some Great Danes. A pattern of less symmetrical white spotting, often called piebald, parti or random

white, is present in many breeds. A DNA variant has been found in Microphthalmia Associated

Transcription Factor- (MITF) gene that is associated with piebald spotting in many breeds.

 

The genetic determination of white spotting in dogs is complex. In breeds such as Collie, Great Dane,

Italian Greyhound, Shetland Sheepdog, Boxer and Bull Terrier, piebald behaves as a dosage-dependent

trait. A dog with one copy of the MITF variant has some white pattern expression, while a dog with 2

copies of the variant display more extreme white with color only on the head and perhaps a body spot.

In Boxers and Bull Terriers, dogs with 2 copies of the MITF variant are completely white and dogs with 1

copy display the mantle (called flash in these breeds) pattern. However, additional mutations in MITF or

other white-spotting genes appear to be present in these breeds that affect the amount of white being

expressed. In other breeds, piebald behaves as a recessive trait- that is 2 copies of piebald are needed to

produce white spotting.

This test will assist breeders with selection of mating that can produce the desired outcome for white.

Results are reported as:

N/N Dog has no copies of piebald

S/N Dog has 1 copy of piebald

S/S Dog has 2 copies of piebald

 

Note- expression of white patterns varies from breed to breed and among individuals within a breed.

This test is specific for the mutation in MITF known to be associated with piebald/random white

spotting.

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