gene. Other human SLC45A2 polymorphisms result in normal pigment variations, specifically fair skin, light eyes, and light hair in Caucasian populations. A presumed knockout mutation in the same gene causes the phenotype of white tigers, which retain black striping though they lack the typical orange background pigmentation. A polymorphism on the mouse SLC45A2 gene is known to be the cause of the underwhite coat color phenotype. The phenotype was first identified in the 1960s, and since then has been mapped successfully. Affected individuals have a reduction in eye and coat pigmentation, and irregularly shaped melanosomes. See also Equine coat color genetics White (horse) Melanism Gray (horse) Dun gene Champagne gene Silver dapple gene Albinism Leucism Lethal white syndrome References Horse coat colors