By contrast, periodic patterns must arise from a mechanism that is specifically programed to be spatially constrained. 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. 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. 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 ticked phenotype refers to the absence of any superimposed pattern, leaving only the banded or ‘ticked’ background color. 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. (2010)) provides new genetic insight.ĭomestic cats have four distinct and heritable coat patterns – ticked, mackerel, blotched, and spotted – that are collectively referred to as tabby markings ( Figure 1). 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. The similar nature but diverse manifestation among these patterns suggests they are formed by a conserved, adaptable, and largely unexplored mechanism. 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 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. 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.
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