White patterning in horses is known as Dominant White or White. There are about 20 different mutations identified that are associated with white patterns, all mutations are found in the KIT gene. Except for W20, most of the known Dominant White mutations arose recently and are restricted to specific lines within breeds. The Coat Colour Dominant White 3 test, tests for the mutation known as W20 in the KIT gene. This test detects two variants (alleles). The allele W20 is dominant.