Cat Genetics Part Three: Understanding Coat Colour Genetics
This article is part of an insightful ongoing series on cat genetics part one and part two. It is highly recommended that you understand the fundamentals of DNA, genes and inheritance before proceeding.
Where Does My Cat’s Coat Colour Come From?
Coat colour inheritance in cats is fascinatingly complex. Kittens usually inherit colours from both parents, but some traits, like the red gene, are sex-linked, appearing only on the X chromosome. This means red colouring behaves differently in male and female cats. Coat colour genes interact in intricate ways, making full scientific explanation challenging. This article aims to provide a thorough understanding, but beginners might prefer to read part four for an easier explanation.
Phenotype vs Genotype in Cat Coat Colour
It's important to differentiate phenotype (the observable coat colour) from genotype (the actual genetic makeup). Sometimes, a cat’s gene expression (genotype) and appearance (phenotype) may not exactly match due to gene interactions and expression variability.
Black Coat Colour Genetics
Black is effectively the base colour for cats. The dominant gene B codes for eumelanin, a black pigment. Only one copy is needed for black coat appearance, which explains why black cats are common, especially in non-controlled breeding such as in moggies. Recessive alleles b and bl produce brown (chocolate) and cinnamon colours respectively when paired.
The Red Coat Colour Gene
The red or ginger colour is controlled by a sex-linked gene on the X chromosome. Unlike males that have one X, females have two, so producing red female kittens requires both parents contributing the gene. The gene codes for phaeomelanin, a red pigment. In males, one copy of the gene (O) makes them red; females need two (OO). If the recessive form (oo) is present, it allows black or its variants to show instead.
Tortoiseshell Cats: The Black and Red Mix
Tortoiseshell cats are almost exclusively female because the red gene is X-linked. These cats carry one red gene and one non-red gene (Oo). Due to X chromosome inactivation, patches of red and black appear in their coats, causing the characteristic tortoiseshell pattern. Male tortoiseshell cats are extremely rare (about 1 in 3000) and usually sterile, often due to an XXY chromosome arrangement.
Dense Pigment and Dilution
The dense pigment gene, often called dilute, controls pigment distribution. The dominant D results in normal dark coats, while the recessive homozygous form (d/d) dilutes the colour – black to blue/grey, red to cream, chocolate to lilac, cinnamon to fawn. This gene is recessive and can lie dormant over generations, sometimes leading to unexpected dilution traits in offspring.
Dilution Modifiers and Amber Pigment
A dilution modifier gene (Dm) is thought to intensify diluted colours, producing caramelised shades such as blue-based caramel. Additionally, a mutation mainly found in Norwegian Forest Cats can change black eumelanin to amber pigment, contributing to unique coat colours in those cats.
The Impact of White Coat Genes
White coat colour overrides other coat genes by preventing pigment cell migration during embryo development, making white cats phenotypically white regardless of underlying genetics. However, white cats may have fewer pigment cells, increasing their risk of skin sensitivity and related conditions. Even one white gene from a parent can produce white kittens, so responsible breeding should consider what coat colours white masks.
White Spotting Gene
Many cats display white patches due to the white spotting gene (S). Only one copy is needed for white areas ranging from small spots to extensive patches like tuxedo or mittens patterns. Different white patterns, such as those seen in Ragdolls or Snowshoes, are believed to come from variations of this gene.
For a simpler and more accessible explanation of cat coat colour inheritance, consider reading part four. To learn about how coat patterns are inherited, see part five.
Cat Genetics Series
