Introduction

Tabby patterning has been present in cats since their domestication. Even the name "Tabby" has a rich history, tracing back to the Silk Road, referencing the "watered" or striped silks manufactured and traded through the Middle East. In the last decade, scientists' understanding of Tabby has undergone significant changes, with the 2010 discovery that Ticked and Tabby reside in different genes, the 2012 discovery of Taqpep as the seat of Tabby, and the 2021 discovery that Dkk4 is the cause of Ticked. Many forms of Tabby have been described, but the two basic forms now recognised are the Striped or Mackerel Tabby, and the Blotched or Classic Tabby. 

Tabby patterning on the face is characterised by a dark "M" on the forehead, with or without dark lines extending from the corners of the eyes across the cheeks and pale "eyeliner" around the eyes. Depending on the type of Tabby, cats may have striped "necklaces," barring on the legs and tail, and vertical striping of the body, sometimes with a horizontal pattern component. Every cat's pattern is unique, so Blotched and Striped types always represent a spectrum of expression, and they can be further modified by several other genes, including Ticked. 

Establishment of pigment patterns in time and space 

It is not surprising, given how visually complex feline coat patterns are, that the development of these patterns is also complex. Two key concepts are necessary to our current understanding: the reaction-diffusion system, which explains how skin can start out uniform but become patterned, and the two-phase pattern development process, which involves pattern establishment of the skin during gestation, and later, pigment modification of that pre-pattern. Specific genes are actors in one or both processes. 

Phase I: skin pattern establishment 

The key players in this step of feline skin development are the Ticked (Dkk4) and Tabby (Taqpep) genes, and all cats will have two alleles for each of these genes. The wild type of the Ticked gene Dkk4 is non-ticked, which allows full Tabby pattern expression. If any non-wild type Ticked variants are present, they will completely or largely suppress the Tabby pattern by "scattering" the Tabby pattern organisation, as we'll learn below.  

Alan Turing, the famous English polymath, dubbed "the father of modern computer science." In his later work, he developed a concept to explain the development of patterns in living things, called "morphogenesis," through chemical reactions which he called the reaction-diffusion system. His initial concept has been developed much further with our greater understanding of genetics, but the idea still applies, and hinges upon the presence of both an activator and an inhibitor. In this case, we're talking about the process of feline skin pattern development, and we now know some of the genes that fill these roles: 

1. The WNT pathway (Wnt genes) functions as an activator of cell development and organisation and hair follicle development. When it is active or overexpressed, hair follicles are more densely packed. 
2. The Ticked gene, Dkk4 functions as a partial inhibitor of hair follicle development, and when it moderately suppresses the WNT pathway, hair follicles are more sparsely spaced and tend to form clusters. 

What does this have to do with Tabby patterns? It turns out that in cats, the gene for Ticked, Dkk4, is turned on for a specific window of time during pattern establishment in all cats, which temporarily changes the skin's thickness and subsequent hair follicle makeup and creates a Tabby or Ticked pre-pattern "memory" in the skin. Here's a basic breakdown: 

• At 19-21 days into gestation, fetal kitten skin is uniform, and Dkk4 expression is nearly undetectable. 
• During days 24-26, Dkk4 expression rapidly increases. 
• Between 25-28 days gestation, fetal kittens develop well-defined thick and thin areas of skin. Thick areas correspond to later dark Tabby bands, and thin areas to lighter pigment-producing areas (in Ticked cats, these dark areas are much smaller and packed together rather than in bands). 
• After 28 days gestation, Dkk4 activity drops off and skin thickness becomes more uniform again. 
• At 49-58 days, well-developed hair follicles are present, and the Dkk4 pattern is now reproduced, but with pigment in the skin and fur.

Reaction-diffusion system in feline skin. Dkk4+ skin represents future dark stripes or areas.

In short, Dkk4, through local activation of the WNT pathway in the thick areas of the skin, and long-range inhibition of WNT in the thin areas, assigns the developing skin's pigment pattern. One remarkable aspect of this discovery is that this skin pre-patterning occurs before any pigment-producing cells or hair follicles are even developed, yet it corresponds to the Tabby or Ticked pattern that develops later. Scientists do not yet understand the mechanism behind how the cells "remember" whether they are dark or light pigment-producing cells, but clearly some kind of imprinting is taking place. 

Free-roaming cat with Ghost Tabby markings

The cat's Tabby and Ticked genotype establishes a permanent pattern memory, either of many small dark areas as with Ticked, or organised into bands as with Tabby. If two copies of Ticked are inherited, Tabby patterns are unlikely to become the established skin pattern in phase one of development. If only one copy of Ticked is inherited, evidence of Tabby can sometimes be seen in residual leg and tail barring and Tabby facial markings called "Ghost Tabby." A modified broken Tabby or a Tabby with very thin, closely spaced stripes can also occasionally be seen. 

Phase II: pigment modification 

Now that the Phase I patterning is complete, the cat's skin will always have the cellular memory of this pattern, but it may be expressed or modified based on additional genes that regulate what the hair follicles produce, within the confines of the pre-assigned pattern of Phase I. Phase II is where Tabby and Agouti come in, as well as Dilution, Red, White Spotting, and Wideband mutations. According to Eduardo Eizirik, Phase II can be defined as: 

"A pigmentation-oriented mechanism that uses information from the preestablished pattern to regulate the synthesis of melanin profiles." (Genetics, 2010) 

In addition to Tabby and Ticked variants, there are several ways in which pigment production (melanin synthesis) could be regulated after the pre-patterning is complete, creating many layers of variation: 

• Tabby type: Blotched or Striped Tabby can be modified further by rosettes or spots, as in Spotted Tabby, or shading, as in Clouded Tabby. It is not known if this occurs in Phase I or Phase II. 
• Pigment type: The “true" melanins, or the dark pigments of Black, Gray, Cinnamon, and Chocolate, or the rufous or reddish phaeomelanins like Red/Orange, Cream, Russet, Carnelian, and Amber can be produced. 
• Pigment switching: Follicles can toggle between dark and red pigments on a time-or age-dependent basis with Agouti, and in Agouti modifiers, as in the case of Wideband mutations leading to colours like Copper, Sorrel, and Sunshine, or patterns like Smoke, Shell, or Shaded that can change the banding of pigment within hairs. 
• Pigment inhibition or restriction: White Spotting and Full White, Dilution, Caramel, and Colourpoint interfere with pigment production, either by inhibiting pigment expression, by clumping the pigment, or by making pigment production temperature sensitive. 

We know that in other wild felids, and in many domestic cat patterns, colour intensity of markings can fade or increase with age as well. This is the case with Bengals, where we know there is incompatibility of wild and domestic cat Agouti alleles that results in age-dependent changed expression in Charcoal (a Bengal-specific Agouti pattern). As Eizirik stated, there is "gradual decoupling [of the] the pigmentation pathways from the underlying pattern." 

Traditional Blotched Tabby patterned cat

Types of Tabby: Blotched vs. Striped

All cats will have a developmental "prepattern" of either Tabby or Ticked embedded in their skin, and assuming no Ticked pattern variants are present, the Tabby Locus associated with the gene Taqpep will determine what kind of tabby the cat could show. 

Classic/Blotched Tabby 

Although the name Classic would lead one to believe that Classic Tabbies are more common, in fact it is the recessive Tabby type, designated as Tab, and is less widespread. It came to be called "Classic" because it was the desirable Tabby type for show in the late 19th and early 20th centuries. Classic Tabby today is more commonly called Blotched or Marbled Tabby. Blotched Tabbies have broader dark colour banding, often with a more horizontal component in a “swirled” or bullseye appearance, and a “butterfly” pattern over the shoulders. 

Striped/Mackerel Tabby 

A Mackerel is a type of fish, and it is said that the narrower, mostly vertical stripes of the Mackerel Tabby resemble the spine and ribs of that fish. Striped Tabby is considered the wild or ancestral type of Tabby and is dominant to Blotched Tabby. Striped or Mackerel Tabby is denoted as TaM. 

Singapura with both Ticked and Agouti pattern

Ticked 

Ticked denotes a type of colour pattern in which no visible dark Tabby banding is present, as it has a “scattering” effect on Tabby. Instead, it highlights dark and light banding of the hairs, if present. The wild type is non-Ticked (ti+), which is recessive to Ticked patterns. Two alleles have now been discovered, TiA and TiCK. Abyssinians and Singapuras are probably best known for Ticked pattern, and it shows off their Agouti banding to great effect. In contrast, the Burmese is also Ticked, but has been selected for the recessive Non-Agouti or Solid Agouti pattern, so that neither Ticked nor Tabby pattern are visible. 

Orange tabby Maine Coon kitten

Epistatic genes: Orange and Colourpoint 

Sex-Linked Orange 

The most common cause of genetic red or orange colouration in cats is X-linked and dominant, designated with the classic allele name O. The mutation is in the Arhgap36 gene and, interestingly, the genetic mutation and mechanism involved is unique to cats. Sex-Linked Orange (O) is epistatic to Solid  (Non-Ticked), meaning whether all-orange, tortoiseshell, or Patched Tabby, all O-carrying cats will show tabby markings in red areas, even if they carry Non-Agouti (a/a), unless they are Ticked pattern. 

This happens because of the pattern establishment discussed above during fetal development. Even in the absence of Agouti, there is still a pattern memory that resides in the skin, and although Sex-Linked Orange suppresses dark pigments, it still allows for upregulation of red or phaeomelanin pigment production, which follows the same pattern dictated by the cat's Tabby and Ticked genotype. 

Tabby-point Siberian

Colourpoint 

Similar to Sex-Linked Orange, Colourpoint selectively prevents the expression of Tabby and Ticked patterns. Because Colourpoint variants Mocha (cm), Siamese (cs), and Burmese (cb) variants have an effect by creating a temperature-dependent pigment production pathway, a cat’s pre-pattern will only be displayed in the cooler areas of the body – the ears, face, legs, and tail. Some cats may show ghost Tabby or Ticked markings on the torso, especially as they age and their metabolism slows down such that the body shows more pigment. Tabbies then become Tabby or Lynx Colourpoints, which can then be further described by the type of pigment expressed, for example: 

• Seal Tabby Point – dark pigmented points 
• LilacTabby Point – dilute chocolate pigmented points 
• Flame/Red Tabby Point – orange pigmented points 
• Tortie/Torbie Tabby Point – dark and orange pigmented points

Spotted Ocicat

Tabby modifiers – spotting, rosettes, and other variations 

A prominent mystery is the genetic basis for spotted patterns, whether it is the random-spotted Egyptian Mau, the regularly-spotted Ocicat, or the rosetted Bengal. Scientists at Stanford University have been studying coat colour pattern development in cats for a number of years and, building off their research on Tabby and Ticked pattern establishment, they believe some of the more than 300 upregulated genes related to Tabby and Ticked pattern may be involved in controlling such patterns. 

Researchers have found that spotting in the Mau and Ocicat is only possible if Mackerel Tabby (TaM/-) is also present, which suggests that spotting in those breeds represents modifier gene(s) to Mackerel Tabby. In experimental crosses of spotted and blotched cats, F1 offspring show intermediate patterns best described as “Broken Mackerel” (Eizirik), similar to that seen in the Pixiebob. This suggests semi-dominance or complex inheritance for spotting. Conversely, Ticking may be necessary for the "servaline" pattern seen in some Savannah cats and their wild progenitor, the African Serval. Given the Ticked variant scatters the otherwise organised Tabby markings, it makes sense that the servaline pattern is characterised by smaller, more numerous spots, but again, the exact genetic mechanism is not understood. 

The Charcoal variation of the Bengal rosettes is due to a genetic incompatibility between the Agouti alleles of the Asian Leopard Cat and domestic cat, so that pattern will only occur in compound heterozygous cats (APb/A), but the variants causing rosetting are yet to be discovered.  

Additional variations on Blotched or Striped Tabbies are also of unknown genetic cause, such as "Candle flame" Toygers as a modified form of Striped Tabby, or Clouded Tabbies as modified Blotched Tabbies. 

As with any other pattern, Wideband variants provide another layer of pattern modification, shifting the established Tabby, Ticked, and Agouti pattern pigment balance either toward darker pigments or toward red pigments, in the case of CORIN variants. 

Final thoughts 

The diversity of feline coat patterns—from the ancestral stripes of the Striped Tabby to the sand-like Ticked Abyssinian—are the beautiful result of a complex, two-phase developmental process.  

By marrying Turing's reaction-diffusion system with modern molecular genetics, science has unlocked how key genetic actors like Taqpep (Tabby) and Dkk4 (Ticked) permanently imprint a cellular "pre-pattern memory" in the skin during early gestation, long before the first hair follicle or pigment-carrying cell even forms. This physical layout is subsequently brought to life in a second phase, in which Agouti, Wideband mutations, Sex-Linked Orange, Colourpoint, and additional modifiers determine the final pigment profile of each hair and the overall pattern of a cat's haircoat.  

While landmark discoveries over the last two decades have mapped the major genetic switchboards of this system, many beautiful cat traits remain a mystery that scientists continue to study. 

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