Many people observe that while dogs and various other animals come in a wide spectrum of brown shades, truly brown cats appear to be uncommon. While cats exhibit an impressive array of coat colors and patterns, the absence of a pervasive, naturally occurring brown can seem puzzling. This article explores the genetic mechanisms that dictate feline coat coloration, explaining why what appears to be brown in cats is genetically distinct from the brown seen in many other species.
The Two Fundamental Cat Coat Colors
All the diverse coat colors observed in cats originate from just two fundamental pigment types: eumelanin and pheomelanin. Eumelanin is responsible for dark shades, including black and various diluted versions of black. Conversely, pheomelanin produces lighter colors, encompassing red, orange, and yellow hues. The amount and distribution of these pigments within a cat’s hair follicles are regulated by specific genes. Melanocytes, specialized cells in the skin, produce these pigments, and the final coat color depends on how they are produced and transferred to the hair. Unlike some other species that possess a distinct, primary brown pigment, cats do not have a separate genetic pathway for a true brown pigment.
How Genetic Variations Create Diverse Hues
Genetic modifications acting on eumelanin can create brown-appearing coats. The B locus, specifically the TYRP1 gene, plays a significant role in modifying black eumelanin. The dominant B allele produces black coloration. However, two recessive variants, the b allele and the b^l allele, lead to lighter, brown-like shades.
The b allele, when inherited in two copies (bb or bb^l), results in a chocolate phenotype, a rich, dark brown sometimes referred to as chestnut. The b^l allele, when present in two copies (b^l b^l), produces a lighter brown, often called cinnamon, which can have a reddish undertone and appear more subtle than chocolate. Both chocolate and cinnamon are essentially diluted or modified forms of black eumelanin, not entirely new pigment types.
Other genes also influence how these colors are expressed. For instance, the agouti gene creates banded hairs, characteristic of tabby patterns. This banding can cause an overall lightening effect on the hair, making black-based tabbies appear distinctly brown due to the distribution of pigments along each hair shaft, contributing to the broad spectrum of feline coat colors.
Distinguishing True Brown from Cat Coat Colors
The perceived “brown” in cats, such as chocolate and cinnamon, fundamentally differs from the true brown found in many other mammals. In species like bears or deer, brown is often a primary pigment, directly produced and expressed. This is because their melanocytes produce eumelanin that naturally manifests as brown, rather than black, without requiring a specific recessive mutation to modify it from black. Early mammals, for example, were predominantly dark brown.
In cats, however, chocolate and cinnamon coats are modified forms of black pigment, not distinct, inherent brown pigments. While visually brown, they result from specific recessive mutations that reduce black eumelanin intensity. A cat requires two copies of these recessive genes to express these brown-like phenotypes.
The genetic makeup of cats does not produce a primary brown color like black or red. The Havana Brown cat, for instance, is a breed known for its solid chocolate coloration, yet this is still a genetically modified black. Therefore, while feline coats can certainly appear brown, they are expressions of altered black pigments, highlighting unique genetic pathways.