Amelanism (also known as amelanosis) is a pigmentation abnormality characterized by the lack of pigments called melanins, commonly associated with a genetic loss of tyrosinase function. Amelanism can affect fish, amphibians, reptiles, birds, and mammals including humans. The appearance of an amelanistic animal depends on the remaining non-melanin pigments. The opposite of amelanism is melanism, an overabundance of melanin.
Amelanism in mammals
The only pigments that mammals produce are melanins...
Amelanism in other vertebrates
Other vertebrates, such as fishes, amphibians, reptiles and birds, produce a variety of non-melanin pigments. Disruption of melanin production does not affect the production of these pigments. Non-melanin pigments in other vertebrates are produced by cells called chromatophores. Within this categorization, xanthophores are cells that contain primarily yellowish pteridines, while erythrophores contain primarily orangish carotenoids. Some species also possess iridophores or leucophores, which do not contain true pigments, but light-reflective structures that give iridescence. An extremely uncommon type of chromatophore, the cyanophore, produces a very vivid blue pigment.[4] Amelanism in fishes, amphibians, reptiles and birds has the same genetic etiology as in mammals: loss of tyrosinase function. However, due to the presence of other pigments, other amelanistic vertebrates are seldom white and red-eyed like amelanistic mammals.
