Cat Genetics Part Three: Understanding Coat Colour Genetics

Cat coat colour genetics is a rich and complex subject. This article builds on our series introduction and moves into the specific genes responsible for creating the wide variety of coat colours observed in domestic cats. For a more accessible overview, see our easy version article. This part covers the technical underpinnings, focusing on the major genes and how they interact.

The Agouti Gene and Tabby Patterns

The Agouti gene determines whether a cat's coat is solid or tabby patterned. Cats with two copies of the non-agouti allele (aa) are solid-coloured, while cats with at least one agouti allele show tabby patterning. A separate Tabby gene then determines the type of tabby pattern: mackerel, classic, spotted, or ticked. Tabby patterns reveal banding along individual hair shafts known as ticking.

Eumelanin and Phaeomelanin

Cat colour relies on two main pigments: eumelanin (black/brown pigment) and phaeomelanin (red/orange pigment). The production of these pigments is controlled by multiple genes, including the Extension gene and the Agouti gene. Mutations in these genes affect the pigment produced, resulting in colours from black and brown to red and cream.

The B Gene: Black, Chocolate, and Cinnamon

The B gene controls the form of eumelanin produced. The dominant B allele results in black eumelanin. The b allele produces chocolate eumelanin, which is a lighter, warmer brown. The bl allele results in cinnamon, an even lighter reddish-brown colour. Cats with two copies of the same recessive allele display the corresponding colour; heterozygous cats (carrying one dominant B) appear black but can carry and pass on the recessive colour gene.

The Dilution Gene

The Dilution gene (D) controls pigment granule distribution in hair shafts. Homozygous dilute cats (dd) have diluted colours: black becomes blue (grey), chocolate becomes lilac, cinnamon becomes fawn, and red becomes cream. Cats with at least one dominant D allele show full colour. A dilution modifier gene (Dm) exists and can produce caramel and apricot tones in some dilute cats—distinct colour effects seen in certain breeds.

White Spotting and Full White

The White Spotting gene (S) controls the presence and extent of white areas in a cat’s coat. Cats with one copy may show small amounts of white, while two copies often result in a largely white coat with coloured areas only on the head or tail, known as Van patterning. Full white coats are caused by the dominant White gene (W), which epistatic overrides all colour. White cats have historically been linked with potential deafness due to gene linkage, particularly in blue-eyed white cats. Different white gene variations produce spot patterns, like the "mittens" of Ragdolls and Snowshoes, or tuxedo and bi-colour patterns.

Pointed Colour Pattern

The pointed colour pattern, characteristic of Siamese-type cats, results from the cs allele at the C (Colour) locus. This allele produces a temperature-sensitive enzyme, so colour develops only in cooler areas of the body such as the face, ears, legs, and tail, while the warmer body remains pale. Cats homozygous for the cs allele are pointed; heterozygous cats may show different patterns depending on other alleles present at the C locus.

Amber and Rufousing

The Amber mutation, mainly found in Norwegian Forest Cats, results from a mutation in the Extension gene that changes black eumelanin to amber pigment. This creates unique coat shades not produced by other genes. Rufousing refers to the red modifier genes that can shift expression of existing colours towards reddish or tawny tones, contributing to the diversity of coat colours within a breed.

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Final thoughts on cat genetics

The science of cat coat colour genetics is detailed and fascinating, reflecting millions of years of evolution and selective human breeding. Key genes—agouti, B, D, S, W, C, and Extension—interact in complex ways to produce every colour and pattern seen in domestic cats. An understanding of these interactions helps breeders make well-informed pairing decisions that support both breed standards and the health of their cats.