Genes Paint A Dog's Coat

The colour of a dog's coat is determined by its genes and how they are expressed. There are about 19,000 genes in a dog's genome, but only a few affect the physical variations in their coats. Each hair follicle is surrounded by pigment cells, which make and transfer the pigment melanin into a developing hair. Dog fur is coloured by two types of melanin: eumelanin (brownish-black) and phaeomelanin (reddish-yellow). A pigment cell can be signalled to produce either colour of melanin.

Eumelanin and Phaeomelanin: the two pigments that determine a dog's coat colour

The colour of a dog's coat is determined by two pigments: eumelanin and phaeomelanin. Eumelanin is a black pigment, while phaeomelanin is reddish-yellow. Each hair follicle is surrounded by many pigment cells, or melanocytes, which make and transfer either eumelanin or phaeomelanin into a developing hair.

Eumelanin

Eumelanin is responsible for black, chocolate brown, grey, or taupe pigmentation in dogs. It can also be found in the nose and eyes (irises), which can be black, liver (brown), isabella (dusty pale brown), or blue.

Phaeomelanin

Phaeomelanin is responsible for tan pigmentation, including all shades of red, gold, and cream. It appears as a deep red (like Irish Setters), light cream, encompassing gold, yellow, and orange. Phaeomelanin does not occur in the eyes or nose; only eumelanin is found in those areas.

Absence of Pigment

The white coat colour in dogs is not caused by any pigment but by cells that are unable to produce any pigment. The whole animal can be affected, similar to albinos, or it can be localized, like the white markings of a coat.

Genes Involved in Pigment Production

The Melanocortin 1 Receptor (MC1R), also known as the Extension locus, is one of the genes involved in the production of these pigments in dogs. Other genes modify how much eumelanin and phaeomelanin are produced, resulting in the variety of colours and patterns found in dogs.

For example, the Brown gene, Tyrosinase-Related Protein 1 (TYRP1), dilutes black pigment to brown but does not affect red pigment. The Agouti gene (ASIP) organizes the distribution of black and red pigments. Beta-defensin (CBD-103), unique to dogs, is responsible for dominant black (K locus). The dilution gene (MLPH) dilutes both black and red pigments.

Loci and Alleles

The specific physical location of a gene on a chromosome is called a locus, and dogs have several loci that affect coat colour. Each dog has two alleles for each locus, and if the two alleles are the same, the dog is homozygous for that specific gene. If the alleles differ, the dog is heterozygous, and the dominant allele will be expressed.

The A locus, also known as the Agouti locus, affects the distribution of both eumelanin and phaeomelanin. The agouti series contains four alleles: ay (sable), aw (agouti/wolf grey), at (tan points), and a (recessive black). The B locus generates a brown dog coat colour, also called liver, and affects only eumelanin, causing all black colours in the coat to turn brownish. The D locus contains a dilution gene that affects both eumelanin and phaeomelanin. The E locus is responsible for almost all non-agouti eumelanin or phaeomelanin patterning in dogs, with alleles that can cause masking, grizzle/domino, normal extension, or recessive red. Finally, the K locus has three genes: dominant black, brindle, and non-solid black, which allows the A locus to be expressed.

Genes: how they affect the production of pigments

Genes play a crucial role in determining a dog's coat colour by influencing the production of pigments. The two primary pigments that dictate hair colour in mammals, including dogs, are eumelanin and phaeomelanin. Eumelanin is a black pigment, while phaeomelanin is reddish-yellow. The interplay of these pigments results in the diverse colours and patterns observed in dogs' coats.

The genes involved in producing these pigments include Melanocortin 1 Receptor (MC1R), also known as the Extension locus, and Tyrosinase-Related Protein 1 (TYRP1). MC1R controls the production of both eumelanin and phaeomelanin, resulting in various colours and patterns. On the other hand, TYRP1 acts as a modifier, specifically diluting black pigment to brown without affecting the red pigment.

Another critical gene is Agouti (ASIP), which orchestrates the distribution of black and red pigments. It ensures that different parts of the dog's body have distinct levels of each pigment, contributing to the coat's overall pattern. Additionally, the Beta-defensin (CBD-103) gene, unique to dogs, is responsible for dominant black colouration.

Furthermore, the Dilution gene (MLPH) plays a role in lightening both black and red pigments. The presence of this gene in a diluted form can result in a paler coat colour. The intensity of pigmentation is also influenced by genes, with some dogs exhibiting deeper shades of red or richer colours due to specific genetic variations.

The genetic basis for coat colour in dogs is complex, and the interaction of multiple genes determines the final colour and patterning. These genes are located on specific loci on chromosomes, and their expression is influenced by the dog's ancestry. By understanding these genetic factors, scientists and breeders can predict and manipulate coat colours in different breeds.

Locus: the specific physical location of a gene on a chromosome

The colour of a dog's coat is determined by how genes are passed from dogs to their puppies and how those genes are expressed in each dog. Each hair follicle is surrounded by pigment cells, which produce and transfer either eumelanin (brownish-black) or phaeomelanin (reddish-yellow) into the developing hair.

The specific physical location of a gene on a chromosome is known as a locus. Each dog has two alleles for each locus. If the two alleles are the same, the dog is homozygous for that specific gene. If the alleles differ, the dog is heterozygous, and the dominant allele will be expressed.

The loci that affect coat colour include the Agouti (A), Extension (E), and Black (K) loci. The alleles at the A locus are related to the production of agouti signalling protein (ASIP) and determine whether an animal expresses an agouti appearance, and, by controlling the distribution of pigment in individual hairs, what type of agouti. The A locus is also known as the Agouti locus. It affects the distribution of both eumelanin and phaeomelanin. The agouti series contains four alleles: ay (sable), aw (agouti/wolf grey), at (tan points), and a (recessive black).

The alleles at the E locus (the melanocortin receptor one gene or MC1R) determine whether an animal expresses a melanistic mask, as well as whether an animal can produce eumelanin in its coat. The E locus is also known as the Extension locus. One of the genes involved in the production of these pigments in dogs is Melanocortin 1 Receptor (MC1R).

The alleles at the K locus (the β-Defensin 103 gene or DEFB103) determine the colouring pattern of an animal's coat. The K locus is also known as the Black locus. It contains a dominant black gene, which is unique to dogs.

Alleles: the different versions of a gene

Alleles are one of two or more versions of a gene. A dog inherits two alleles for each gene, one from each parent. If the two alleles are the same, the dog is said to be homozygous. If the alleles are different, the dog is deemed heterozygous.

Each hair follicle is surrounded by many melanocytes (pigment cells), which make and transfer the pigment melanin into a developing hair. Dog fur is coloured by two types of melanin: eumelanin (brownish-black) and phaeomelanin (reddish-yellow). A melanocyte can be signalled to produce either colour of melanin.

The genes associated with coat colour are:

• The Brown (B) locus, which affects the colour of the eumelanin pigment produced, making it either black or brown. There are four known alleles that occur at the B locus: B = Black eumelanin; b = Brown eumelanin.
• The Dilution (D) locus, which determines the intensity of pigmentation. There are two common alleles: D (normal, wild-type MLPH), and d (defective MLPH).
• The Intensity (I) locus, which determines how intense the phaeomelanin (red) pigment is, and so determines whether a dog is white, yellow, gold or red.
• The Agouti (A) locus, which affects the distribution of both eumelanin and phaeomelanin. The agouti series contains four alleles: ay (sable), aw (agouti/wolf grey), at (tan points), and a (recessive black).
• The Extension (E) locus, which determines whether an animal expresses a melanistic mask, as well as whether an animal can produce eumelanin in its coat. There are three known, plus two theorised, alleles that occur at the E locus: Em = Mask (a eumelanin mask is added to the face); EG = Grizzle (tan underparts with a dark overlay covering the top and sides of the body, head and tail); Ed = Northern Domino (found mostly in Northern breeds such as the Siberian Husky); E = Normal extension (pattern expressed as per alleles present at A and K loci); eh = Cocker sable; e = Recessive or clear fawn (tan, inhibition of eumelanin).
• The Black (K) locus, which determines the colouring pattern of an animal's coat. There are three known alleles that occur at the K locus: KB = Dominant black (black); kbr = Brindle (black stripes added to tan areas); ky = Phaeomelanin permitted (pattern expressed as per alleles present at A and E loci).

Genotype and Phenotype: the combination of alleles that a dog has, and the physical appearance impacted by the genotype and/or environment

The colour of a dog's coat is determined by its genes and how they are expressed. Dogs have about 19,000 genes in their genome, but only a handful affect the physical variations in their coats. Each hair follicle is surrounded by many pigment cells, or melanocytes, which make and transfer the pigment melanin into a developing hair. Dog fur is coloured by two types of melanin: eumelanin (brownish-black) and phaeomelanin (reddish-yellow).

Genotype refers to the combination of alleles that a dog has at a particular locus. A locus is the specific physical location of a gene on a chromosome. Each dog has two alleles for each locus, one inherited from each parent. If the two alleles are the same, the dog is homozygous for that specific gene. If they are different, the dog is heterozygous. Phenotype refers to the physical appearance impacted by the genotype and/or environment.

The B locus, for example, controls whether a dog's coat is liver-coloured (brown). This locus will determine if black pigment in the coat, nose, paw pads, and eyes is lightened to brown pigment. A dog with the genotype BB or Bb will have a black coat, while a dog with the genotype bb will have a brown coat.

The E locus (MC1R) has four alleles which can be reported: Em, Eg, E, and e. The E allele provides the ability to make eumelanin in the coat and is dominant to the e allele (recessive red). Dogs that are ee (recessive red) will not produce any dark hairs.

The K locus (CBD103) has two reported alleles: KB and ky. KB is dominant black, meaning that only one copy of KB is needed for the coat colour to be expressed. If a dog has at least one KB allele, the A locus will not be expressed.

The A locus (ASIP) has four alleles that can be reported: ay, aw, at, and a. The ay allele (fawn or sable) is dominant to all other A alleles, and aw (agouti or wolf sable) is dominant to at (black and tan) and a (recessive black).

The D locus (MLPH) will determine if eumelanin in the coat, nose, paw pads, and eyes is "diluted" to blue or isabella. For 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.

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.

Together, these genes account for the variation in coat colour seen in dogs.

Frequently asked questions