Coat color genetics can be fun and interesting at the same time.
This is because there seems to be an exception to every rule, and the veterinary genetics community still has much to discover about coat color. Learning about the inheritance of coat colors can be incredibly rewarding, as it allows one to see the power and influence of genetics in real time, creating a visual model to better understand the genetics of health disorders and breed-specific traits.
Embark hopes to make coat color easier to understand by providing the following information and this infographic. If you need help, you can contact a member of the customer experience team at breeders@embarkvet.com.
Basic Genetic Terminology
Locus: The location of a gene or variant within a dog’s genome or DNA (plural is loci)
Wild-type: The most common genotype observed in a natural population at a specific location in the dog’s genome
Variant: A difference in the DNA compared to wild-type, at a specific location in the genome
Genotype: The combination of wild-type and variant loci that an organism carries. A dog inherits two copies of every gene, one from each parent. If a dog has two copies of a gene or variant that are the same, then the dog is said to be homozygous at the gene or variant, whereas if the dog has one copy of a variant, the dog is said to be heterozygous
Phenotype: The physical appearance resulting from the genotype at one or multiple loci, which can also be influenced by the environment
Recessive: Two copies of a variant are needed to express the phenotype
Dominant: Only one copy of a variant is needed to express the phenotype
Incomplete dominance: Incomplete dominance occurs when both variants or a variant and a wild-type genotype, are partially expressed, often resulting in an intermediate or different phenotype. It is also known as partial dominance.
Coat, Nose, Paw Pad, and Eye Color Pigment
For a dog, all black or brown (“liver”) areas are caused by cells producing eumelanin (black/brown pigment). However, there are genes that change the structure or production of eumelanin, changing the phenotype to brown, blue, or isabella. Brown is caused by a change in the structure of eumelanin, blue is a diluted black pigment, and isabella is a diluted brown pigment.
Phaeomelanin is a reddish-yellow pigment produced in the coat. It does not occur in the eyes or the nose; only eumelanin occurs in those areas so only genes that affect eumelanin can affect their color. You will learn more about phaeomelanin when we discuss the E locus.
What Embark Reports for the E, K, A, B, and D Loci
The E locus (MC1R)
The E locus (MC1R gene) allows dogs to make eumelanin in their coats. Variants or mutations in this gene can disrupt the production of eumelanin in various ways. The MC1R gene has seven known genetic variants Em, Eg, Ea, Eh, e1, e2, and e3. Embark is already testing for the Em, Eg, and e1 variants, and we have recently added Ea, Eh, e2, and e3.
An MC1R gene without these variants is denoted as E, or ‘wild-type.’ The MC1R variants have a hierarchical dominance pattern. Em (melanistic or dark mask) is at the top of the hierarchy meaning that it is dominant to all of the other MC1R variants. Em results in the phenotypic expression of a dark facial mask as seen in the German Shepherd Dog and Pug breeds, and this phenotype will be expressed with either one or two copies of Em.
Eg (grizzle) causes the phenotype of a widow’s peak in the Afghan Hound and Saluki breeds and was originally thought to be next in the hierarchy and dominant over wild-type E (Dreger et al 2010). However, a recent study (Honkanen et al 2024) suggests that E is, in fact, dominant over Eg, while other unpublished studies as well as our own observations suggest that E is incompletely dominant over Eg, i.e. the phenotype of Eg is only sometimes expressed, likely due to other unknown variants segregating.
Wild-type E has been shown to be dominant over the Ea and Eh variants, which have similar phenotypes to Eg but differ with respect to the breeds in which they occur. Ea has been found in the Siberian Husky and Malamute breeds, and Eh has been found to cause the ‘sable’ phenotype in the English Cocker Spaniel which looks like the widow’s peak of the Afghan Hound and Saluki breeds
Finally, in the hierarchy are the three known e variants: e1, e2, and e3, which cause the ‘recessive red’ phenotype when homozygous (two copies of any of the e variants). The wild-type E variant is dominant to e1, e2, and e3, i.e. dogs that are EE or Ee can produce dark (black, brown, blue, isabella) hairs, but their distribution will be dependent on the genotypes at the K and A loci.
Dogs that have two copies of any of these e variants, i.e. are ‘ee,’ will not produce any dark hairs regardless of their genotype at the K, A, B, and D loci. Interestingly, you can usually tell the genotype at the B and D loci in ‘ee’ dogs by the color of a dog’s nose. The shade of red in ‘ee’ recessive red dogs can range from a deep copper coat color in Irish Setters to a yellow coat in Labrador Retrievers to the white coat color of Samoyeds. This variation in red coat color intensity is controlled by multiple other variants and depends on the breed.
The K locus (CBD103)
The two reported variants at the K locus (CBD103) are KB and ky. Embark does not report brindle (sometimes abbreviated as Kbr), because currently there is insufficient evidence supporting the genetics of brindle for Embark to accurately report this test. KB is dominant to ky. This means only one copy of KB is needed for the coat color to be expressed. We use the term dominant black for KB. If a dog has at least one KB variant, you can completely ignore the A locus regarding that dog’s phenotype. In a breeding animal, however, it may be important to know the A genotype. If a dog is kyky (and not ee), the A locus will be expressed as follows.
The A locus (ASIP)
The A locus (ASIP) has 4 variants that can be reported: ay, aw, at, and a. Unlike the K locus which has one dominant and one recessive variant, the A locus has a dominance hierarchy like the E locus. The ay variant (fawn or sable) is dominant to all other A variants and aw (agouti or wolf sable) is dominant to at (black and tan) and a (recessive black). The at variant is only dominant to a. However, this dominance hierarchy may not apply to all breeds.
For example, using the standard hierarchy above, a dog that is ayaw or ayat will be fawn/sable, and only a dog that is atat or ata will be black and tan. It has been thought that the variants are not additive and an awat dog and an awaw dog will both be the same degree of wolf sable, however, feedback from many breeders suggests that there may be breed-dependent interaction of the A variants. There are also several different coat patterns for fawn/sable dogs which goes beyond the scope of this article. Like with the K locus, both variants may be important to record to know what your breeding dog may produce.
Next are the B and D loci. Both will lighten pigment, and the variants at the B and D loci are recessive in their phenotypic expression. This means two copies of the recessive genotype (b or d) must be phenotypically expressed.
The B locus (TYRP1)
The B locus (TYRP1) will determine if the black pigment in the coat, nose, paw pads, and eyes is lightened to brown pigment. Embark tests for four TYRP1 variants; TYRP1_bc, TYRP1_bd, TYRP1_bs, and the recently added TYRP1_bn. Dogs need at least two copies (bb) of any of these variants for black hairs to become brown and for the dog’s eyes to be amber or copper. Brown, chocolate, or liver are all breed-specific phenotypic terms used to describe bb. Some breeds refer to the brown phenotype as red, but genetically speaking, red is used for phaeomelanin and not eumelanin.
The D locus (MLPH)
The D locus (MLPH) will determine if eumelanin in the coat, nose, paw pads, and eyes is “diluted” to blue or isabella. Embark tests for the three known MLPH variants; MLPH_D1, MLPH_D2, and MLPH_D3. For the dilute or dd dogs, noses can be any shade from light to deep charcoal grey, and their eyes can range from light brown, yellow, yellow-green, or grey.
What does the term isabella mean? It is a special term for dilute brown (bbdd). This is the color often associated with Weimaraners.
What Embark Reports for the S locus
The S locus (MITF)
The S locus (MITF) controls where pigment is produced in a dog’s coat and skin. An insertion near the MITF gene turns off pigment production in the coat and skin, resulting in white hair and/or pink skin. Dogs with two copies of the insertion (sp) will likely have breed-dependent white patterning, with a nearly all white, parti, or piebald coat. Dogs with one copy of this variant will have more limited white spotting and may be considered flash, parti, or piebald.
It is important to note that the MITF insertion variant does not explain all white spotting patterns in dogs and other variants are currently being researched. For example, some dogs may have small amounts of white on their paws, chest, face, or tail, regardless of their S Locus genotype. This is referred to as residual white. Dogs of some breeds are fixed for Irish spotting, a pattern of white undersides, often a white neck collar, and sometimes white facial markings. Research into the genetics of Irish spotting is ongoing.
What About Mate Selection and Expected Litter Coat Color?
When approaching coat color genotype to determine phenotype, it is best to go step by step with an individual dog. You can use Pair Predictor, an automated prediction calculator, in your My Embark for Breeders dashboard to determine base coat color, base patterns, and pigment for any sire or dam in your account or watch a tutorial on Punnett squares to visualize coat color genetics for a potential mating.
