• DOI:10.1111/j.1755-148X.2010.00723.x
• Corpus ID: 7082692

Tabby pattern genetics – a whole new breed of cat

@article{Kaelin2010TabbyPG,
  title={Tabby pattern genetics – a whole new breed of cat},
  author={Christopher B. Kaelin and Gregory S. Barsh},
  journal={Pigment Cell \& Melanoma Research},
  year={2010},
  volume={23}
}

• C. Kaelin, G. Barsh
• Published 1 August 2010
• Biology
• Pigment Cell & Melanoma Research

Much of what we know about pigment cell biology comes from studying laboratory mice, yet the conservation of gene action and interaction across domesticated animals, including horses, cattle, pigs, and dogs, is firm evidence that most aspects of color variation are conserved in mammals. The domestic cat, however, is a special case in which variation within and among breeds exhibits a fascinating glimpse into an entirely new area of color variation as exemplified by tabby patterns. Periodic patterns with color markings spaced at non-random intervals are common in nature and evident in all major mammalian orders – stripes on chipmunks, reticulated markings on giraffes and hyenas, tail rings on lemurs, and, of course, tabby stripes on domestic cats. The similar nature but diverse manifestation among these patterns suggests they are formed by a conserved, adaptable, and largely unexplored mechanism. Periodic patterns are conspicuously missing from the laboratory mouse, but the cat stands out as a unique genetic model in which recent work from Eizirik et al. (2010) provides new genetic insight. Domestic cats have four distinct and heritable coat patterns – ticked, mackerel, blotched, and spotted – that are collectively referred to as tabby markings (Figure 1). These patterns are a composite of two features: (i) a light background component resulting from individual hairs with a subapical light-colored band and (ii) a superimposed darker component resulting from unbanded hairs. The ticked phenotype refers to the absence of any superimposed pattern, leaving only the banded or ‘ticked’ background color. Mackerel, blotched, and spotted phenotypes describe variations of the tabby pattern, in which the darker component forms either periodic vertical stripes (mackerel), whorls (blotched), or leopard-like spots (as in the Ocicat or Egyptian mau breeds of domestic cats). The periodicity of tabby markings distinguishes them in a fundamental way from other characteristic but randomly displayed markings, such as the tricolor patches on a calico cat or the black spots on a Dalmatian. These random patterns arise from events that are stochastically initiated (like inactivation of an X chromosome in females or survival of a melanocyte cluster) but stably maintained, either through epigenetic mechanisms as with X inactivation, or a developmental process, as with a limited window for neural crest migration. By contrast, periodic patterns must arise from a mechanism that is specifically programed to be spatially constrained. What are the molecules and cells that underlie tabby patterns? A genetic approach to this question began nearly a century ago when Phineas Whiting described three tabby ‘banding factors’, noting a simple pattern of inheritance for each: ticked is dominantly inherited relative to mackerel and blotched, whereas blotched is recessively inherited relative to ticked or to mackerel (Whiting, 1918). Whiting posited a single locus (T ) with three alleles – ticked (T ), mackerel (T ), and blotched (t ). That view has now been revised by the recent work of Eizirik et al. (2010), who applied a genome-wide panel of molecular markers to pedigrees segregating the different coat color patterns, and thereby discovered that two loci were involved in determining the difference between ticked, mackerel, and blotched patterns (Figure 1). In this modern view of cat pattern genetics, the Tabby locus determines the type of pattern, with the Ta (Mackerel) allele dominant to the Ta (Blotched ) allele, while a second locus, now known as Ticked, determines the absence or presence of pattern, with the Ti A allele dominant to the Ti allele. The nomenclature has become complicated; similar to Eizirik et al. (2010), we use lower case roman to describe the