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Basic Genetics of Dog Coat Colours

Dog lovers and breeders alike appreciate the fascinating array of coat colours and patterns that make each breed unique. These variations are not simply aesthetic; they hold the key to understanding the complex genetic code that shapes our canine companions.

Whether you are a seasoned Border Collie breeder or an amateur Cavoodle breeder, learning more about this topic can help breeders make better decisions regarding how to improve their chosen breed both in terms of appearance and health.

The Basics of Canine Color Genetics

Before we begin, let’s revisit some basic genetics. Dogs, like humans, have 23 pairs of chromosomes that contain thousands of genes. These genes, made up of DNA, act like a blueprint for every trait a dog possesses, including its coat colour. Each gene has multiple variations, or alleles, and dogs inherit one allele from each parent.

Dog coat colour is primarily determined by two genes: the Extension (E) gene and the Agouti (A) gene. The B (Brown), D (Dilution), and K (Dominant Black) genes can modify these basic colours. Each gene has a pair of alleles, which can be either dominant or recessive.

Dominant alleles exhibit their trait even when only one copy is present, while recessive alleles require two copies, one from each parent, to display their trait. For instance, the dominant allele for black colour (B) will override the recessive allele for brown (b), resulting in a black coat, even if a dog carries the brown allele.

The Extension (E) and Agouti (A) Genes

The E gene impacts whether a dog will have a yellow coat or a black/brown coat, and it has three possible variants: EM (mask), E (extension), and e (recessive yellow). If a dog has even one E or EM allele, it can produce black pigment, assuming it doesn’t carry two copies of the recessive brown (b) allele.

The A gene, on the other hand, dictates the distribution pattern of the black and yellow pigments. The variants in order of dominance are: ay (fawn/sable), aw (wolf/agouti), at (black-and-tan), and a (recessive black). An “ay” dog can appear yellow, even with E in its genetics, because “ay” overrides the distribution of black pigment.

Modifying Genes: B, D, and K

The B gene influences pigment intensity. The dominant variant (B) enables black pigment, while the recessive variant (b) produces brown pigment in both skin and hair, but only if there are two copies.

The D gene dilutes black pigment to blue (grey) and red/yellow to cream, while the K gene, with two variants (KB and ky), regulates the relationship between the E and A genes. A dog with at least one KB allele will be solid black (or brown or blue, depending on B and D), regardless of the E and A genes.

The Influence of Sex on Dog Coat Color

Interestingly, there is a group of genes, the S locus, or “spotting” genes, that are not entirely understood but relate to white spotting on dogs. They seem to follow a pattern similar to the X-chromosome inactivation in female mammals, but more research is needed.

In terms of sex influence on coat colour, X-linked genes can cause a difference in coat colour between males and females, although this is rare in dogs. One example is seen in the “tortoiseshell” coloration observed in some breeds, which appears only in females. This is because the genes for red and black colour are on the X chromosome, and males only have one X chromosome.

Health Implications of Coat Color

Finally, it’s crucial to understand that certain coat colours and patterns can be associated with health issues. This is due to pleiotropy, where a single gene controls more than one physical trait, including susceptibility to certain diseases.

For instance, dogs with the merle pattern, a result of a variant M allele, can suffer from abnormalities regarding hearing and sight, particularly if they are homozygous merle (MM). Similarly, white dogs, especially those with the double recessive sw allele, are more likely to be deaf, and breeds with the dilution gene (d) are prone to Colour Dilution Alopecia, a condition leading to hair loss and skin problems.

Dalmatians are a distinctive example: their unique coat pattern is associated with a gene that causes high uric acid levels, leading to urinary stones.


Understanding the genetics of dog coat colour offers more than a fascinating delve into biology. It can aid breeders in predicting the coat colours of potential litters and provide insights into the potential health implications for specific breeds and colours. While our understanding is continually evolving, each discovery underscores the remarkable interplay of genes that create the canine rainbow of colours and patterns we so admire.

In the hands of responsible breeders, pet owners, and scientists, this knowledge can be used to prioritise the health of our beloved canine companions, ensuring that they not only look good but feel good too. As science continues to unravel the intricacies of genetics, we move closer to a world where every dog, regardless of its coat, can lead a healthier, happier life.

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