Understanding Canine Coat Color Genetics

by Dr. Mikel Delgado, PhD

There are several genes that contribute to your dog’s outward appearance - but perhaps the most obvious are those related to your dog’s coat color.

All dog coat colors start with two basic pigments, those for black (eumelanin) and red (pheomelanin). The coat colors we see are a modification of these pigmentation cells (called melanin). Multiple genes contribute to the alteration of the cells that create these pigments, making them lighter or more intense and controlling how they are combined to form the full spectrum of dog coat colors and patterns, from white and cream to orange, brown, and gray (and beyond)!

How coat colors develop

Although there are at least 15 genes related to coat colors and patterns, eight of them are especially important in contributing to your dog’s coat color. These genes may have unique effects, or may combine with other genes to produce the color or pattern. Each gene can have multiple alleles or variants, and as you will see, the relationships between some of these genes can be quite complex.

Variants

Each gene has multiple alleles (variations, also known as variants) - your dog will inherit one variation from each of their parents, and those two alleles create the combination that gives them their coat color. For example, if a dog inherits two copies of the recessive “d” (dilute) allele, they will have a lighter, dilute color.

In coat colors, a dominant variant is usually indicated by a capital letter (e.g., M for Merle), and the recessive variant is indicated by a lowercase letter (m for non-merle).

For more information, check out our glossary of genetic terms and article on modes of inheritance!

A (Agouti gene)

The expression of the agouti gene is partially dependent on the E, K, and B genes. There are several variants of the A gene, which can result in shading and the appearance of bands of different colors. Most variants of the A gene result in a fawn coat, a “wolf” sable coat, or a tri-color (including black and tan) coat. Dogs who inherit two copies of the recessive form (aa) of the agouti gene will not express agouti, and will either be black or bicolor. 

B (Brown gene)

The brown gene determines whether a dog will be brown or black. The dominant B allele will lead to a black coat, and the recessive b will create chocolate, brown, and liver colors when the dog inherits two copies. However, in order for bb to be expressed as brown, the dog must also have at least one copy of the dominant E (extension) gene that produces eumelanin. If the dog is also ee on the E locus, their coat color will not be affected by the B gene, although they will have brown nose and foot pads if they are also bb.

Note: The B gene is not the only one that can cause some dog breeds to have brown coats.

D (Dilute gene)

A mutation in the D gene results in an incomplete distribution of melanin cells, resulting in a lightened coats (e.g., from black to gray). Typical coat colors that are due to the dilute gene include fawn, lilac, and “blue”. Dilute is a recessive trait, meaning that a dog typically must inherit the dd allele pattern for the lightening of the coat to be expressed.

Because dilute coats are not part of every breed standard and in some breeds can be associated with hair loss (alopecia) and skin problems, it is recommended to test breeding dogs for the dilute gene. A dog who is Dd will not appear dilute, but is a carrier of the dilute gene and will pass it on to their offspring. If two Dd dogs are bred, on average, 25% of their puppies will be dd and could have skin problems associated with this genotype. 

E (Extension gene)

The extension gene is responsible for the black mask of some dogs, and the solid yellow coat of others. It has seven known variants, three of which are common and are believed to be present in dogs early in the process of breed selection/formation.The E variant is dominant and responsible for the production of eumelanin. The e variant is recessive and shuts down the production of eumelanin while causing cells to produce phaeomelanin. A dog with EE will be black, and a dog with ee will be a variation of yellow, red, or white. A dog who is Ee will appear black, but carry the yellow gene, which may be passed down to offspring.

Em codes for black and also controls the presence of the “melanistic mask” - the black mask observed on many dogs, such as German Shepherds and Pugs. It is a dominant trait, and so a dog only needs one copy of the Em allele to have a black mask. If the dog is black, the mask is hidden but can be passed to offspring.

H (Harlequin gene) 

The harlequin gene is responsible for the spotted appearance of some Great Danes. H interacts with the merle (M) gene, by turning areas of fur between the black merle patches completely white. If there’s no dominant merle allele present, there is no effect of the harlequin gene - the dog will have a typical coat coloring without the harlequin effect. The inheritance pattern is autosomal dominant, so heterozygous dogs (Hh) will show a harlequin coat pattern if there is a dominant merle allele.

The homozygous allele pattern HH is considered to be embryonic lethal (meaning that puppies would die in the womb), because it is not observed in living dogs. It is assumed that all dogs with the harlequin coat pattern are heterozygous (Hh).

K (Dominant Black gene)

The K gene has three different alleles, or variants. Kb is the dominant black allele that inhibits the expression of the A (agouti) gene – because it is dominant, only one copy of the Kb allele is enough to cause dogs to have a black coat. 

The Kbr allele allows the A gene to be expressed, but the agouti pattern will be brindled. If a dog has the Kb allele and the Kbr allele, they will still be black, as the Kbr allele is recessive to Kb.

The third allele is Ky, and it allows the A gene to be expressed without brindling. Ky is recessive to both Kb and Kbr; A dog who is Kb/Ky will be black, and a dog who is Kbr/Ky will be brindle. The coat color of a dog who is Ky/Ky will be determined by the agouti gene!

M (Merle gene)

The merle gene is responsible for patches of both solid and diluted colors, as is often seen in Australian Shepherds, Shelties, and Collies (in some breeds, this pattern is referred to as “dapple”). The merle gene can also impact eye, nose and paw pad coloration.

There are two alleles, m (non-merle) or M (merle). The M allele can be different sizes, represented by a number between 200 and 280. The larger the number, the longer the allele, and the greater the likelihood that a merle pattern will be displayed. Dogs with the shorter alleles are often referred to as “cryptic” or “phantom” merles because the merle pattern may not be present in the coat, even though the gene is there.

The effects of the M gene are also affected by the E (eumelanin) gene, which allows for the expression of black pigment. Dogs with ee will generally have lighter patches than those who are Ee or EE.

Merle genetics are quite complicated, but there are a few important things to know:

• Homozygous merles (MM) are at higher risk of certain health problems, especially of the ears and eyes. 
• Two merle dogs (even if Mm or cryptic) should not be bred together, as they increase the risk of producing MM puppies).
• Merle only occurs naturally in a small number of breeds. The recent introduction of the merle gene through crossbreeding may result in merle dogs where merle is not part of the breed standard.

S (Piebald/Spotting gene)

The S gene controls coat patterns with white patches such as parti and piebald. This gene inhibits the production of melanin in skin cells. The resulting white patterning can vary greatly, from white spotting, to large patches, to a dog who is mostly white.

Depending on breed, the S gene can be recessive or have incomplete dominance. A dog with two piebald S alleles will display some extent of white patterning. A heterozygous Ss dog may or may not have white patterning. A dog with two non-piebald alleles will not have piebald markings, although they may have white fur due to other genes. 

Negative health outcomes associated with coat color

Some coat colors are associated with negative health outcomes. This is typically due to a dog inheriting two copies of a recessive allele. See our article on modes of inheritance for more information on what this means!

Dilutions (D): Some dilute dogs are affected by alopecia (hair loss) and skin problems. 

Merle (M): The merle gene is dominant (M). A dog with one copy of the dominant merle allele is at higher risk for hearing and vision abnormalities compared to non-merle dogs. For “double merles” (MM) the risks are even higher for developmental, eye, and ear abnormalities.

Harlequin (H): A double-harlequin dog will die before they are born (in utero), resulting in smaller litter sizes or maternal complications.

White markings (S): Dogs with large amounts of white hair, such as dalmatians and some piebalds, may be born deaf.

Albinism: Albinism in dogs is caused by a rare mutation that causes a lack of pigmentation. Albino dogs are sensitive to the sun, and may be susceptible to skin cancer. 

Breeding decisions and coat colors

Decisions around breeding dogs based on their coat color genetics can be complicated (or for some breeds, not an issue at all!). We encourage all breeders to research the standards for their breed, and if DNA testing for coat color genes is warranted. In some breeds, with associated health risks, these test results should be incorporated into breeding decisions. 

Further resources

Good Dog Webinar: Genetics of Dog Coat Color and Traits with Dr. Casey Carl, DVM

VCA: Genetics Basics: Coat Color Genetics in Dogs

Brancalion, L., Haase, B., & Wade, C. M. (2021). Canine coat pigmentation genetics: a review. Animal genetics. https://onlinelibrary.wiley.com/doi/10.1111/age.13154 

Schmutz, S. M., & Berryere, T. G. (2007). Genes affecting coat colour and pattern in domestic dogs: a review. Animal genetics, 38(6), 539-549. https://pubmed.ncbi.nlm.nih.gov/18052939/

Webb, A. A., & Cullen, C. L. (2010). Coat color and coat color pattern-related neurologic and neuro-ophthalmic diseases. The Canadian Veterinary Journal, 51(6), 653. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2871368/