The bottom row depicts the influence of the white spotting ( S) locus on the size and appearance of color patches in female cats that are heterozygous at the O locus. A female O/O, A/A or O/O, A/a would be indistinguishable from an O/O, a/a cat. No phenotype for the agouti locus is given for cat ādā as orange is epistatic over nonagouti. From left to right: (a) nonorange, wild-type agouti (b) nonorange, nonagouti (c) orange heterozygote, nonagouti (d) orange homozygote. Genotypes are presented for a female with representative coat color. The top row depicts variation at the orange locus. ![]() (A) Phenotypic variation at the orange locus. The resulting orange phenotype is likely caused by the exclusive presence of pheomelanic pigments in the hair shaft ( Figure 1A). Orange controls an unknown molecular mechanism that causes the suppression of black-brownish pigmentation (eumelanin) in favor of orange-yellowish coloration (pheomelanin) ( Vella et al. This locus has attracted the attention of geneticists for over a century ( e.g., Doncaster 1904 Wright 1918). Other genes involved in domestic cat pigmentation remain unknown, including the X-linked orange ( O) locus ( Searle 1968 Vella et al. Pigmentation genes have been identified on the basis of comparative genetic data supported by genetic linkage or association studies. THE domestic cat displays a broad diversity of phenotypic variation, including an array of coloration patterns resulting from interacting genotypes at multiple loci. Furthermore, epistasis of orange over nonagouti was demonstrated at the genetic level. Haplotype analysis revealed potential recombination events that could reduce the size of the candidate region to 3.5 Mb and suggested multiple origins for the orange phenotype in the domestic cat. Fine mapping placed the locus between markers at positions 106 and 116.8 Mb in the current 1.9Ć-coverage sequence assembly of the cat genome. This detailed linkage map was applied to position the X-linked orange gene, placing this locus on the q arm of the X chromosome, as opposed to a previously reported location on the p arm. Extreme variation in recombination rates (centimorgans per megabase) was observed along the X chromosome, ranging from a virtual absence of recombination events in a region estimated to be >30 Mb to recombination frequencies of 15.7 cM/Mb in a segment estimated to be <0.3 Mb. ![]() Microsatellite markers with an average spacing of 3 Mb were selected from sequence traces of the cat 1.9Ć whole genome sequence (WGS), including the pseudoautosomal region 1 (PAR1). A comprehensive genetic linkage map of the domestic cat X chromosome was generated with the goal of localizing the genomic position of the classic X-linked orange ( O) locus.
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