Penetrance of this mutation was incomplete and age-dependent. The large number of asymptomatic carriers and the good prognosis support the interpretation of benign disease.

SummaryFive feline-derived microsatellite markers were genotyped in a large pedigree of cats that segregates for ventral white spotting. Both KIT and EDNRB cause similar white spotting phenotypes in other species. Thus, three of the five microsatellite markers chosen were on feline chromosome B1 in close proximity to KIT; the other two markers were on feline chromosome A1 near EDNRB. Pairwise linkage analysis supported linkage of the white spotting with the three chromosome B1 markers but not with the two chromosome A1 markers. This study indicates that KIT, or another gene within the linked region, is a candidate for white spotting in cats. Platelet-derived growth factor alpha (PDGFRA) is also a strong candidate, assuming that the KIT-PDGFRA linkage group, which is conserved in many mammalian species, is also conserved in the cat.Keywords cat, feline, KIT, PDGFRA, spotting, white.White spotting pelage and skin phenotypes have been investigated in a variety of mammals. In cats, the white spotting locus (S), appears to affect melanocyte migration. Heterozygous animals (Ss) have a ventral white pattern (Whiting 1919), not spots, as the name would suggest. This ventral white pattern, known as bicolour by cat fanciers, is considered to be dominant to solid colour, with an additive effect of the dominant allele. Full solid colour (ss) is recessive, while the van pattern, in which colour is limited to the head and tail regions, is postulated as homozygous SS (Kuhn & Kroning 1928). Various other white spotting phenotypes show spotting at the ventral midline, such as lockets and belly spots, or white at the extremities, such as gloves and mittens. These other white presentations are anticipated to be allelic to ventral white (Whiting 1919). In addition, dominant white (W), which is associated with blue eye colour and deafness in the cat, may be allelic to white spotting (Whiting 1919;Bergsma & Brown 1971); however, epistasis has complicated allele assignments.The gene(s) responsible for white spotting in the domestic cat have not yet been identified. In several mammals, mutations in loci including EDNRB, KIT and PDGFRA (Smith et al. 1991;Stephenson et al. 1991Stephenson et al. , 1998 have been shown to be causative for the dominant white and/or the white spotting phenotypes. We hypothesized that mutations in EDNRB, KIT, or PDGFRA control at least one type of white spotting pattern in the domestic cat, and we performed a linkage analysis of ventral (bicolour) white spotting using a panel of five microsatellites spanning these three genes.An extended pedigree of 114 cats segregating for white spotting (Fig. S1) from the WALTHAM Centre for Pet Nutrition (Melton Mowbray, Leics, UK) was used for the linkage analysis. Three white spotting cat phenotypes were assigned according to the white pattern grading system proposed by Robinson (1959): solid, bicoloured and van (Fig. 1). Solid coloured cats had no evidence of white spotting. Bicolour cats had a ventral white pattern with approximately 50% or more of the coat having pigm...

Many genes influencing mammalian coat colours are well conserved. While genes responsible for pelage phenotypes in one species provide strong evidence for a candidate gene in a different species, the X-linked orange phenotype of the domestic cat is unique within mammals. The orange locus (O) undergoes X-inactivation, producing females that express both wildtype black (wt) and orange (variant) phenotypes when heterozygous (tortoiseshell). The orange locus has not yet been localized on the X chromosome. Tortoiseshell male cats have been identified but have been shown to be sex chromosome trisomies (XXY). To localize the cat orange locus, 10 feline-derived X-linked microsatellites were analysed in two extended cat pedigrees consisting of 79 and 55 individuals, respectively, segregating for the orange phenotype. Linkage analyses excluded close association of orange in the vicinity of the nine informative X-linked microsatellites. One marker was not polymorphic within either family. Several markers suggested exclusion (Z < -2.0) at distances of 7.5-33 cM. Exclusion analyses suggested a possible location for orange a 14 cM region near Xcen. Recombination distances of markers in the segregating feline pedigrees were reduced as compared with the feline interspecies backcross family. Thus, the presented pedigrees may be useful as reference families for the domestic cat because more accurate recombination rates for domestic cats can be determined.

SummaryThe Tabby markings of the domestic cat are unique coat patterns for which no causative candidate gene has been inferred from other mammals. In this study, a genome scan was performed on a large pedigree of cats that segregated for Tabby coat markings, specifically for the Abyssinian (T a -) and blotched (t b t b ) phenotypes. There was linkage between the Tabby locus and eight markers on cat chromosome B1. The most significant linkage was between marker FCA700 and Tabby (Z ¼ 7.56, h ¼ 0.03). Two additional markers in the region supported linkage, although not with significant LOD scores. Pairwise analysis of the markers supported the published genetic map of the cat, although additional meioses are required to refine the region. The linked markers cover a 17-cM region and flank an evolutionary breakpoint, suggesting that the Tabby gene has a homologue on either human chromosome 4 or 8. Alternatively, Tabby could be a unique locus in cats.

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