Genetic basis of Agouti - The Agouti locus in cats regulates the ASIP (Agouti Signaling Protein) gene, which plays a critical role in coat colour by influencing pigment type production within hair follicles. The typical (dominant) A allele produces a banded hair pattern (agouti) seen in tabby coats. The recessive a allele results from mutations that prevent normal ASIP expression, allowing continuous eumelanin production and producing a solid (non-tabby) coat colour. Cats must be a/a homozygotes to fully suppress the agouti banding pattern. Other coat colour and pattern genes at unrelated loci (such as O – Orange, B – Brown, E – Extension, Mc – McTabby, Wb – Wideband, Ti – Ticked, and C – Colourpoint) interact with the Agouti locus to determine a cat’s final appearance.
Pathophysiology - ASIP expression in hair follicles is temporally and spatially regulated during hair growth: When ASIP is active, it binds to the melanocortin-1 receptor (MC1R) in melanocytes, switching pigment synthesis from eumelanin (black/brown) to phaeomelanin (yellow/red). When ASIP is inactive, melanocytes revert to producing eumelanin. In agouti-patterned hairs, this switching occurs partway through hair growth, producing banded hairs that create tabby patterns. In a/a solid-coloured cats, ASIP activity is absent or disrupted during hair development, so hairs contain only eumelanin or, in orange areas, only phaeomelanin.
Complications - The Agouti gene alone does not cause health problems — its “complications” are purely aesthetic and genetic-breeding related: Phenotypic suppression of tabby markings in a/a cats means breeders must be aware of “hidden tabbies” (cats genetically carrying other tabby pattern alleles but not expressing them). Interactions with other coat genes can mask or modify agouti expression (e.g., wideband can lighten agouti bands; colourpoint can override visible banding).
Why This Matters to Breeders and Vets - Breeders use knowledge of the Agouti gene to plan matings for specific coat patterns and to avoid unexpected “tabby bleed-through” where faint markings appear in solid cats. Genetic testing for agouti status can reveal whether a solid cat carries the dominant A allele. Veterinarians benefit from understanding this genetic mechanism when advising on coat colour breeding genetics, identifying certain breeds or lines, and explaining to owners why a cat has its particular patterning. The Agouti gene also has research importance in pigmentation biology as ASIP is conserved across species.
Summary - The Agouti gene in cats controls coat colour banding by regulating the ASIP gene’s expression, which switches melanocyte pigment production between eumelanin (black/brown) and phaeomelanin (yellow/red). Dominant A alleles produce agouti banding patterns (tabby), while recessive a/a cats produce solid colours without tabby markings. Coat colour outcome is a result of interaction between Agouti status and multiple other pigment genes. Although it has no health consequences, understanding the Agouti gene is essential for precision breeding, genetic testing, and explaining feline coat variation.