A-Locus Cat (Agouti, Charcoal, Tabby, Ticked)

A-Locus Cat (Agouti, Charcoal, Tabby, Ticked)

The formation of the classic tabby pattern in cats – a dark striped or spotted pattern on a paler background – is governed by the Agouti (A) Locus. The A-Locus corresponds to the agouti signalling peptide (ASIP) gene. ASIP is responsible for the distribution of dark and light melanin (pigment) in the hairs of mammals.

Cats carrying the un-mutated version of the A-Locus allele, designated as “A”, are capable of forming a natural tabby pattern. Cats affected by the A-Locus mutation known as Non-Agouti, or “a” have a solid, un-striped coat instead.

Another, more complex mutation on the A-Locus is specific to the Bengal cat and causes what is known as the Charcoal coat pattern. Charcoal results in distinctive dark markings: a “mask” along the forehead, nose and around the eyes; and a “cape” that goes down the length of the back with a “ghost” pattern visible beneath. Charcoal Bengals have dark grey, brown or carbon-coloured fur, with little to no visible red. The Charcoal mutations, designated as A^pbe, are believed to derive from the Asian Leopard Cat (Prionailurus bengalensis), which was hybridized with the common domestic cat to create the Bengal breed.

A third set of mutations relevant to a tabby coat doesn’t occur directly on the A-Locus, but on the gene Laeverin (LVRN), also known as Transmembrane aminopeptidase Q (Taqpep). The so-called Blotched Tabby or Marbled mutations cause a merging and thickening of tabby stripes, resulting in a pattern of large, dark marbled whorls.

Likewise, a dominant mutation to the gene for the dickkopf WNT signaling pathway inhibitor 4 (DKK4) can also alter the typical tabby pattern. This mutation, found in the Abyssinian cat, is responsible for that breed’s distinctive sandy coat pattern, known as “Ticked”. Ticked cats have a more evenly-blended coat pattern than other tabby cats, with a colour distribution often described as “sand-like” or “salt-and-pepper”. In some cases, faint striping (ghost stripes) may still be visible on the lower legs, face and tail. As with all forms of tabby, a ticked coat is only possible if the cat is not affected by the non-agouti mutation.

Inheritance

The Non-Agouti mutation (a) is autosomal recessive in inheritance. The blotched tabby mutations are likewise autosomal recessive. The different blotched tabby mutations are equivalent; a cat will display a blotched tabby coat if it has two copies of one mutant allele, or one copy of two different mutant alleles each. The blotched tabby patterns are only visible if the cat also displays one or two A-alleles on A-locus.

Charcoal colouration in Bengal cats and related breeds inherits in a specific, autosomal semi-dominant manner: only cats with one copy of the Apb-allele and one copy of the A-allele will display a charcoal coat.

Relevant tests

• K378
• K407
• K476
• K757