The white tiger pelage is an autosomal recessive trait determined by a designated white (W) locus (genotype w/w)1,3; the golden color is another autosomal recessive trait coded by an independent locus termed wideband (WB, referring to a wider central part of the hair shaft; genotype wb/wb)2; and the snow white pelage is a polygenic trait determined by dual-recessive effects at both the white and wideband loci (genotype “w/w; wb/wb”)2. The missense mutation p.A477V in SLC45A2 has been shown to cause the background coloration switch in white tigers4. The only reported mammalian wideband gene thus far is the agouti signaling protein (ASIP) gene in deer mice5, but whether the wideband gene of the golden tiger is ASIP, and the mechanism of interaction between the W and WB loci leading to the snow white pelage remain elusive. Resolving the feline wideband gene would be the ultimate step towards elucidating the genetic basis of all known coat color morphs in tigers.

Morphological examination categorizes tiger hairs into long, straight guard hairs or short, curled zigzag underhairs. Different tiger coat color variants exhibit a consistent pattern in hair composition whereby 90% of hairs are zigzag hairs, which predominantly contribute to pelage coloration. Zigzag hairs from the orange background of a wild-type tiger are agouti-patterned with sub-apical pheomelanin bands and dark tips and bases, and the stripes are uniformly black (Figure 1A and Supplementary information, Figure S1A). In contrast to the wild type, zigzag hairs from a golden tiger's background fur are agouti hairs but with prolonged, lighter-colored sub-apical pheomelanin bands and dark tips/bases consistent with a “wideband” phenotype (Figure 1A-1B and Supplementary information, Figure S1A); those from the stripes are solid reddish brown. Pigmentation alteration in the golden tiger suggests a role of the WB locus in extending the pheomelanin synthesis phase during the hair growth cycle. Spectrophotometric measurement showed a significant decrease in eumelanin content in the golden tiger's background zigzag hairs compared to the wild-type (Supplementary information, Figure S1B), which is consistent with the observed reduced degree of black pigmentation (Figure 1B).

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