A major gene that causes a cat to have a white coat is a dominant masking gene, an allele of KIT which suppresses pigmentation and hearing. The cat would have an underlying coat colour and pattern, but when the dominant white gene is present, that pattern will not be expressed, and the cat will be deaf. A cat that is homozygous (WW) or heterozygous (Ww) for this gene will have a white coat despite the underlying pattern/colour.