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Canine Coat Color

VetGen DNA CHROMAGENE Coat Color Testing

For many years geneticists and breeders have been aware of several locations on the chromosomes, or loci, which are responsible for the color patterns we see in dogs and other mammals. As with all genetic traits, every animal inherits one copy of each locus from each of its parents. Each of these loci is responsible for one or more traits either independently, or in conjunction with another locus. All of them act on the pathways that produce the two major pigments, phaeomelanin and eumelanin, or affect the distribution of those pigments.

The combined effect of all these loci (Agouti, Brown, Extension, etc.) is the color of the dog. Due to the complex interactions of these genes, it is possible for dogs to carry hidden colors which may appear in their offspring. Over the past several years, scientists at VetGen and elsewhere have determined the actual genes associated with many of these loci, and identified the mutations responsible for the different versions (alleles) of these genes. The fruit of this work are the tests available for many of the common coat colors and traits.

The diagram below illustrates the relationships among the major loci (A, B, E and K) involved in determining coat color. The sections that follow describe the role these loci and others play in the coat color tests that VetGen offers. These tests demonstrate that while a dog may exhibit certain color or colors, it may also be carrying other hidden colors in its genetic code that can show up in later generations.

How do the A, B, E, and K loci affect each other in determining coat color?

The accompanying graphic helps to illustrate the interactions of the genes at these four loci in a hierarchy in terms of their role in coat color. If a circle is filled with color, it means the color of the dog has been determined at that point. If a circle is still white, it means information about an additional gene is required.

How do the A, B, E, and K Loci affect each other in determining coat color?

The first locus to look at is the E locus. The gene at this locus is responsible for black masks when present as well as most shades of yellow and red. Any dog that is "ee" will be some shade of yellow to red, and everything happening at the A, B, and K loci will be hidden until the next generation. If the dog has any E or Em alleles, then it will not be yellow and we must look next at the K locus.

There are three versions, or alleles, of the K locus: KB, kbr, and ky. If a dog has even a single copy of KB (KBKB, KBky, KBkbr) it will be solid colored in the pigmented areas, and we go directly to the B locus to determine color. Everything happening at the A locus in these dogs is hidden until the next generation. If a dog is kyky, it will not be brindled, and we go next to the A locus to see which alleles are expressed. If a dog is kbrkbr, or kbrky, it will nearly always be brindled and we look next at the A locus to see the background color and pattern of that brindling.

The A locus has at least four alleles. There are direct tests available for Ay (fawn or sable),"a" (recessive black), and "at" (tan points). There is no direct test for the Wild type (think wolf pattern) allele which is designated aw.Any dog which has at least one copy of Ay (and no KB) will be fawn or sable, either with or without brindling.Any dog that is "aa" (and no KB) will be black. Any dog that is atat or ata (and no KB) will have tan points, either with or without brindling.

The next stop is the B locus. Any dog which is "bb" will be have brown fur in those areas that would otherwise be black. This holds true for both solid colored and agouti-patterned animals.

The D locus (not shown in the diagram) can alter the intensity of pigment. Animals which are "dd" exhibit grey or blue fur in place of black, and light tan or "Isabella" in place of brown. This tan is similar to some AY shades but lacking any banding or black tips on individual hairs.

AVAILABLE TESTS

E locus

The E locus is responsible for the black mask seen in many breeds, and more significantly, for the presence of the yellow to red coats of many dogs. The gene involved is known as MC1-R, which has at least three versions affecting the appearance of the dog, E, Em, and e. Dogs with two copies of e will be yellow, orange or red in their pigmented coat regardless of their genotype at all the other loci

Research at VetGen and independently at the University of Saskatchewan has identified two new alleles in the E locus, Eg and Eh. These mutations are responsible for a reverse mask or widow's peak appearance in the "domino" Afghan Hound and "grizzle" Saluki (Eg), as well as the "sable" English Cocker Spaniel (Eh). Research continues to determine if they are responsible for similar appearance in additional breeds.

Test for "e"

Analysis proves absence or presence of the mutation typically responsible for yellow, lemon, red, cream, apricot and some white in at least the following breeds and all dogs with these breeds in their lineage:

Afghan, Australian Cattle Dog, Australian Shepherd, Border Collie, Beagle, Brittany Spaniel, Cardigan Welsh Corgi, Chinese Shar-pei, Chow Chow, Cocker Spaniel, Dachshund, Dalmatian, Doberman Pinscher, English Cocker Spaniel, English Setter, English Springer Spaniel, Field Spaniel, Flat-Coated Retriever, Foxhound, French Bulldog, German Longhaired Pointer, German Shepherd, German Shorthaired Pointer, German Wirehaired Pointer, Irish Setter, Labrador Retriever, Lowchen, Pointer, Pomeranian, Poodle, Pudelpointer.

Test for Em

Analysis reveals whether a dog with a mask has one or two copies of this version of the extension locus. Animals with a single copy can produce offspring with or without a mask, while those with two copies will only produce masked offspring. The test may also be applied to black dogs where it may not be possible to tell if there is a mask. It may be present in the following breeds and all dogs with them in their lineage:

Afghan, Belgian Shepherd, Boxer, Bull Mastiff, Cairn Terrier, Cardigan Welsh Corgi, Chihuahua, Chinese Shar-pei, English Bulldog,German Shepherd, Great Dane, Greyhound, Lakenois, Pekinese, Pug, Saint Bernard, Saluki, Staffordshire Bull Terrier,Whippet.

Test for Eg and/or Eh

Analysis reveals the absence or presence of the mutations responsible for "grizzle" in Salukis and "domino" in Afghans (Eg) or "sable" and "dirty red" in English Cocker Spaniels (Eh).

B Locus

The B locus is responsible for the presence of brown, chocolate, or liver animals. It is also responsible for nose color. The gene associated with this locus is known as TYRP1. In breeds where the A locus does not come into play, any animal that has at least one B allele (and is not "ee"), will be black in pigmented coat. Those dogs, which have two copies of any of several b alleles will be brown. There are at least three such b alleles. Regardless of other loci, any animal with at least one B allele will have a black nose and pads, while those with any two b alleles will have a liver nose and pads.

Test for b

This test analyzes whether an animal has 0, 1 or 2 copies of the mutations typically responsible for brown, which is also known in some breeds as liver, chocolate, sedge, and less frequently, red. There are three primary "b" mutations that are responsible for nearly every liver or chocolate dog. A notable exception is the French Bulldog where in addition to these three mutations, there is a fourth cause of chocolate that has yet to be identified.

It can be present at least, but not exclusively, in the following breeds:

Australian Cattle Dog, Australian Shepherd,Bedlington Terrier, Border Collie, Brittany Spaniel,Cardigan Welsh Corgi, Chihuahua, Chinese,Shar-pei, Cocker Spaniel, Curly Coated Retriever,Dachshund, Dalmatian, Doberman Pinscher,English Cocker Spaniel, English Setter,English Springer Spaniel,Field Spaniel, Flat-Coated Retriever, Fox Terrier, French Bulldog,German Longhaired Pointer, German Shorthaired Pointer, German Wirehaired Pointer,Labrador Retriever, Lowchen,Miniature Pinscher,Newfoundland Pointer, Pomeranian, Poodle, Portuguese Water Dog, Pudelpointer,Scottish Terrier, Skye Terrier,Weimaraner, Wirehaired Pointing Griffon.

Also:
Any dogs that contain these breeds in their lineage.

K Locus

The K locus plays a pivotal role in coat color. This locus is a relative newcomer in our understanding of canine color, and includes traits formerly attributed by some to other genes.

The dominant allele in the series is KB, which is responsible for self-coloring, or solid colored fur in pigmented areas. This trait was formerly attributed to the Agouti (A) locus as AS, but recent breeding studies had shown this not to be the case.

There are two other alleles, kbr, and ky. KB is dominant to both kbr and ky, while kbr is dominant only to ky. kbr is responsible for the brindle trait and for a long time had been considered to belong in the E locus. Recent breeding studies had also shown this to be incorrect. The recessive allele, ky, allows the basic patterns of the A locus to be expressed. So too does the kbr allele, but with brindling of any tan, fawn, or tawny areas.

Any animal with at least one KB allele will be self-colored.

Any animal with at least one kbr allele, and no KB allele will be brindled on agouti background (see A locus).

Any animal with two ky alleles will show agouti patterns (see A locus).

The mutations responsible for these alleles were identified and described primarily by Sophie Candille in the laboratory of Dr. Greg Barsh at Stanford University.

Test for KB and ky

Vetgen can presently test for these two alleles. In some breeds, where no brindle is present, this represents a complete analysis of the locus. An example would be the Pug. In breeds where the breed standard disqualifies all but self-colored dogs, testing for these two alleles is once again all that is needed. Any animal with two KB alleles cannot produce anything except self-colored offspring. A prime example here is the Labrador retriever. In breeds where many variations are allowed, these tests can help predict the probability of potential litters to include fawn, sable, tawny, tan point, tricolor or recessive black puppies.

KB KB self-colored (solid color in pigmented areas)
KB kbr self-colored (solid color in pigmented areas)
KB ky self-colored (solid color in pigmented areas)
kbr kbr allows A locus to express (tan point, tricolor, fawn, sable, tawny) with brindling
kbr ky allows A locus to express (tan point, tricolor, fawn, sable, tawny) with brindling
ky ky allows expression of agouti patterns without brindling

A Locus

The A locus is responsible for a number of common coat patterns in the dog. Expression of all of them requires any combination of two ky or Kbr alleles at the K locus, and at least one E or Em allele at the E locus.  The gene involved is the Agouti gene, and variations in it are responsible for fawn and sable dogs (Ay), wild type (aw), tan points (at), and recessive black(a).

Test for Ay

Analysis proves absence or presence of the mutation typically responsible for fawn or sable. In fawn/ sable dogs this test shows if other agouti alleles are present but hidden (only one copy of Ay). It also demonstrates how many copies of this allele are hidden in dogs, which cannot express agouti types (KBKB, KBkbr, KBky, at the k locus and/or "ee" at the E locus).

Test for “a”

Analysis shows whether a black dog is black due to “recessive black,” or the more common black at the K locus. It also reveals whether a non-black animal carries “recessive black.”  Examples of breeds:

German Shepherd Dog, Shetland Sheepdog, Belgians (Tervuren, Malinois,Lakenois, Groenendael).

Test for “at

Vetgen is now offering a test for a mutation that is found in all tan point, phantom, tricolor, and "black/tan, chocolate/tan and liver/tan" dogs. This mutation, at, was identified and reported by researchers at the University of Saskatchewan.

In order to produce “at” pups, the pups need to inherit both an at and a ky or kbr allele from both parents, but no KB . In many breeds where the occasional tan point dog is viewed as unwanted, the k test is still warranted since the majority of dogs have two copies of this at mutation, but do not express it because of the presence of an overriding KB.

The “at” mutation is also found in recessive black dogs, but does not cause recessive black (a). In breeds that do not have recessive black (most breeds), this test alone will indicate the presence of “at”. In breeds where recessive black is present, “at” can be determined by using this test in conjunction with the recessive black test, or by our previous process of elimination approach of testing for Ay and recessive black.

It should also be noted that recessive black is present at a very low frequency in more breeds than we once thought (ie French Bulldogs, Poodles and Tibetan Mastiff).

Testing for this mutation along with Ay and recessive black (a) also allows for the identification of aw alleles in those breeds where it is present.In breeds where only the Ay and at alleles are present, the Ay test can be used to see if the fawn/sable dog is Ay/Ay (homozygous) or only has one Ay (heterozygous). If it only has one, the other allele must be at (ie Afghans,Collies,Cardigan Welsh Corgi, Dachshund, Norwich Terrier, Staffordshire Terrier).

In breeds where only Ay, a and at alleles are present, both the Ay test and the "a" test need to be performed. Any alleles unaccounted for by these two tests will be at. For example, if a dog is Ay/Ay both alleles are accounted for. If a fawn/sable dog only has a single Ay, then the other allele must either be an "a" or an at and this can be determined by running the recessive black ("a") test or the at test (ie Shetland Sheepdog, Belgian Shepherd (Tervuren, Malinois, Lakenois, Groenendael).

D Locus

The D locus is the primary locus associated with diluted pigment, which results in coats that would otherwise be black or brown instead showing up as gray, or blue in the case of black, and pale brown or Isabella in the case of brown. The melanophilin gene has recently been shown to be responsible, but not all of the dilute causing mutations have been identified yet.

M Locus

The M locus is responsible for the merle and double merle color patterns seen in some breeds. The mutation which causes merle in all of its forms has been identified. VetGen cannot offer a test for merle because it is patented elsewhere.

Coat Length

While it is not a color trait, the length of a dog's coat is of interest to many. It has recently been demonstrated that in many breeds, the FGF5 gene is responsible for whether a dog has a long coat (rough or fluffy), or a short (smooth) coat. The test Vetgen offers detects the presence or absence of the recessive allele that results in long coats when present in two copies, and as such allows dogs with short coats that carry a hidden "long coat" allele to be detected. In addition to the original coat length mutation, research at VetGen has identified some new mutations present in northern breeds (Akita, Chinook, Siberian Husky) that are responsible for the "woolly" long coat. These new tests are offered exclusively through VetGen.

Furnishings

Furnishings refer to the longer facial hair around the eyebrows, moustache, and beard commonly seen in many breeds, including the wirehaired breeds. Presence of furnishings is dominant to the unfurnished version of the gene, which depending on breed may also be referred to as satin, or sleek. VetGen offers a test to see if a furnished dog carries the recessive unfurnished trait, which is considered unfavorable in some breeds.

Curly

The gene responsible for curly coat has also been identified. Most breeds are fixed for either curly or not-curly, but in breeds where there is variation, dogs may now be tested to see if they carry zero, one or two copies of the curly or non-curly versions of the KRT71 gene.