Cats from all over the world display a great variety in expressions of cat coat colour and for this reason were always a subject of research in fields of genetics and inheritance. Influence of certain genes on the cat’s coat colour can be relatively easy to explain, while some of them may be more complicated than expected. The reason for this is because genes do not act in isolation, independently from other genes. In the following article, we will mention some of the main loci recognized that affect the coat colour, and explain they influence on the phenotype, as well as their influence on the expression of other cat coat colour genes.
The cat coat colour, eye, and skin colour is a result of present pigments. Two main pigments responsible for the coat colour and eumelanin, which is seen as a black or intense brown pigmentation, and phaeomelanin, recognised a red-yellow pigmentation.
Cat Coat Colour Genetics
A locus, also known as the agouti, affects the distribution of both pigments, eumelanin and phaeomelanin. The wild type gene of the A locus, A gene, is dominant in the series and it causes the agouti shift phenomenon, resulting in hairs to be differently pigmented at the tips and at the roots, such as in tabby stripes. The colour shift varies from from expression of eumelanin to phaeomelanin. Tabby stripes are determined by the tabby gene (T).
The recessive gene on the locus prevents this pigmentation shift, and when it is inherited in a homozygous form (aa genotype), it results in black pigment production through the whole hair growth cycle. For this reason, the aa genotype masks the tabby pattern.
Agouti cat with tabby pattern
B locus stands for ”black” since the dominant gene of the locus is expressed in the black coat colour. Genes of the B locus influence the expression of only eumelanin. Two mutations of the B gene have been identified, b (brown or chocolate) and bl (light brown or cinnamon). The chocolate (b) allele is dominant over the cinnamon (bl) allele. Since the B gene is dominant over the locus, cats heterozygous for it ( Bb or B bl genotype), carry chocolate or cinnamon gene but it cannot be recognized based on phenotype.
A mutation at the D locus results in coat colour dilution when both present alleles are mutated. Such genotype can be recognized as Blue, Lilac and Fawn phenotype. The reason for this colour dilution is the clustering of the pigment particles in the hair shaft. Blue is the dilute form of Black; it is commonly seen as various shades of gray. Lilac is the dilute form of Chocolate; it is described as dove or light grey and is sometimes called lavender. Fawn is the dilute form of Cinnamon; it is described as a caramel colour.
Influence of the D locus genes on the black coat color: black and blue cat
Orange, or the O gene, is located on the X chromosome, and is, therefore, sex-linked trait. There are two types of alleles of the O gene, the orange (O) allele, and the non-orange (o) allele. The O gene is dominant, and when present, it leads to phaeomelanin production and inhibition of the black pigment. As an X-linked gene, males can be O or o, while females can be OO, Oo, and oo. Male O and female OO cats are red in colour, while Oo females are known as calico, with red and black pigmentation present in the coat colour. The orange gene on O locus has not yet been identified.
When possessing orange and black coat color genes, a male cat will express only the orange coat color. A female cat with both coat color genes will be recognized as a tricolor or calico cat.
The colourpoint pattern is commonly associated with Siamese cats but can appear in the domestic cats as well. The C locus genes belong to the so-called Albino series and are in following hierarchical order: C (full colour) > cb (Burmese) = cs(Siamese) > c (complete albino). The C gene, also known as the Himalayan gene, codes for the tyrosinase enzyme, which is necessary for the production of melanin. Mutations in the C gene result in phenotypes with different degrees of pigmentation, as a result of a temperature sensitive mutation in the metabolic pathway from tyrosine to pigment. This is results in better pigment production at the extremities, which are cooler, such as the face, tip of the tail and paws, and therefore look darker than the warmer body parts.
Burmese cats are recognized by their dark sepia brown coat colour which is a result of the cb gene. Although this colour is typical for the Burmese cat breed, not all Burmese possess this gene.
Siamese cats exhibit coat color typical for the temperature sensitive mutation within the C locus, which results in better pigment production at the colder extremities, which are cooler, such as the face, tip of the tail and paws.
Albino cats are recognized by the white coat and blue eyes. The albino mutation causes a premature stop codon in the tyrosinase gene. The mutation is recessive and the albino cats are homozygous for the mutation. Since the tyrosinase gene is essential in multiple biochemical pathways, albino cats are usually deaf. Cats heterozygous for the albino gene are not completely albino and have one eye pigmented, a phenotype also known as the ‘’odd-eyed’’. Such cats are usually deaf only on one ear, the one closer to the albino blue eye.
The white cat coat colour is a result of an absence of any pigmentation. Totally white cats can be expressed as a phenotype of 3 different genotypes: albino (cc genotype), totally white spotted cats (SS genotype), and dominant white gene (WW or Ww genotype).
The W, or white masking gene inhibits the normal production of pigment cells during the embryologic development. Since the W gene is dominant, when cat possesses one or two copies of the W allele, it will be white regardless of other coat colour genes it carries. The white cats with the W allele have been linked to deafness.
Turkish Van is a famous odd-eyed cat breed.
The white spotting gene varies in its expression and usually causes only partially white coat. Sometimes the white spotting can be so strong, that the whole coat will be white. Homozygous cats (SS genotype) tend to have bigger white areas than the heterozygous cats (Ss genotype).
Knowing family tree can help you in predicting the future cat coat colour, but since certain recessive traits can be masked by dominant colours throughout generations, it is not possible to know with 100% accuracy. DNA testing enables full insight into your cat’s genetic heritage and reveals possibilities of future kitten’s coat colour, depending on the parents. AnimaLabs currently offer DNA tests for A locus (Agouti), B locus (Brown ), C locus (Colour Point), D locus (Dilution), E locus (Extension), W locus (White).
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Schmutz, S. (2017) Genetics of Coat Color in Cats, Emphasizing DNA studies. A brief review. University of Saskatchewan.
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