 Three genotypes possible with the "S" (white spotting) gene, with capital "S" standing for a wild-type copy and lower-case "s" standing for the mutant.The lack of tabby striping in bicolor cats is controlled by the agouti protein, which inhibits the production of melanin and thus prevents the formation of dark hair colors.In agouti cats the gene is turned on and off as the hair grows, producing hairs with alternating stripes yellow and black.