Cat Coat Genetics - Genes Involved in Fur Pattern and Shading

Genes Involved in Fur Pattern and Shading

• The agouti gene, A/a which codes for agouti signaling protein. The dominant, wild-type A causes the agouti shift phenomenon which causes hairs to be black pigmented at the tips and orange pigmented at the roots (revealing the underlying tabby pattern), while the recessive non-agouti or "hypermelanistic" allele, a, prevents this shift in the pigmentation pathway. In its homozygous form, aa, this results in black pigment production throughout the growth cycle of the hair. Thus, the non-agouti genotype (aa) masks or hides the tabby pattern, although sometimes a suggestion of the underlying pattern can be seen (called "ghost striping"), especially in kittens. The O allele is also epistatic over the aa genotype. That is, the A to a mutation does not have a discernible effect on red or cream colored cats, resulting in these cats displaying tabby striping independent of their genotype at this locus. This explains why you can usually see the tabby pattern in the orange patches of non-agouti tortoiseshell cats, but not in the black or brown patches.
• The primary tabby pattern gene, Mc/mc, sets the basic pattern of stripes that underlies the coat: the basic wild-type tabby gene, Mc, produces what is called a mackerel striped tabby (stripes look like thin fishbones and may break up into bars or spots); while a recessive mutant, mc, produces a blotched or classic tabby pattern (broad bands, whorls, and spirals of dark color on pale background usually with bulls-eye or oyster pattern on flank), common in Iran, Great Britain and in lands that were once part of the British Empire and Persian Empire.
• Secondary tabby pattern genes such as Ta / ta, at which locus a dominant mutation produces an Abyssinian ticked or non-patterned agouti tabby, having virtually no stripes or bars. (This is one type of unpatterned tabby; the other type of unpatterned tabby is the shaded/chinchilla. See inhibited pigment gene, below.) The dominant ticked tabby allele masks all other tabby patterns.
• Other genes (pattern modifier genes) are theorized to be responsible for creating various type of spotting patterns, many of which are variations on a basic mackerel or classic pattern. There are also hypothetical factors which affect the timing and frequency of the agouti shift, affecting agouti band width and the number and quality of alternating bands of eumelanin and phaeomelanin on individual hairs.

Tabby cats (AA or Aa), normally have:

• M on forehead. (Visible in ticked tabby cats, but hard to discern in shaded silver/golden, and tipped cats)
• Thin pencil lines on face. (Visible in ticked tabby cats, but hard to discern in shaded silver/golden, and tipped cats)
• Black "eyeliner" appearance and white or pale fur around eyeliner.
• Pigmented lips and paws.
• A pink nose outlined in darker pigment
• Torso, leg, and tail banding. (Torso banding disappears in the ticked tabby.)

Most or all striping disappears in the chinchilla or shaded cat, but you can still identify the cat as a tabby from these other features.

• There is an interesting gene, not yet identified but believed to be related to the agouti gene, in the Chausie breed, that produces silver-tipped black fur similar to Abyssinian ticked fur. The "grizzled" phenomenon is purported to have been inherited from the hybridization of domestic cats to Jungle Cats.
• The inhibited pigment gene, I/i. The dominant allele (I) produces tipped hairs that are fully colored only at the tip and have a white base. This allele appears to interact with other genes to produce various degrees of tipping, ranging from deeply tipped silver tabby to lightly tipped shaded silver and chinchilla silver. The inhibitor gene interacts with the non-agouti genotype (I-aa) to produce the color known as smoke. The homozygous recessive genotype when combined with the agouti gene (iiA-), produces tabby coloration, which can vary along a spectrum ranging from a deeply patterned brown tabby, to a lighter "golden tabby", to the very lightly colored shaded or chinchilla golden colors. Orange cats with the inhibitor gene (I-O-) are commonly called "cameo".

The genetics involved in producing the ideal tabby, tipped, shaded, or smoke cat is complex. Not only are there many interacting genes, but genes sometimes do not express themselves fully, or conflict with one another. For example, the melanin inhibitor gene sometimes does a poor job blocking pigment, resulting in an excessively gray undercoat, or in tarnishing (yellowish or rusty fur). Likewise, poorly-expressed non-agouti or over-expression of melanin inhibitor will cause a pale, washed out black smoke. Various polygenes (sets of related genes), epigenetic factors, or modifier genes, as yet unidentified, are believed to result in different phenotypes of coloration, some deemed more desirable than others by fanciers.

Here are the genetic influences on tipped or shaded cats:

• Agouti gene.
• Tabby pattern genes (such as Ta masking the tabby pattern).
• Silver or melanin inhibitor gene.
• Factors affecting the number and width of bands of color on each hair (such as the hypothetical wide band gene).
• Factors affecting the amount and quality of eumelanin and/or phaeomelanin pigment expression (such as theorized rufousing factors)
• Genes causing sparkling appearance (such as glitter in the Bengal, satin in the Tennessee Rex, grizzle in the Chausie).
• Factors to clear up residual striping (hypothetical Chaos, Confusion, Unconfused, Erase, and Roan factors).