page_title: Albinism
section_title: Mechanism and frequency
hierarchical_section_title: Albinism / Mechanism and frequency
caption_attribution_description: English: This hedgehog has no pigmentation due to a genetic mutation.
context_page_description: Albinism is the "congenital absence of any pigmentation or coloration in a person, animal or plant, resulting in white hair, feathers, scales and skin and pink eyes in mammals, birds, reptiles, amphibians and fish and invertebrates as well." Varied use and interpretation of the terms mean that written reports of albinistic animals can be difficult to verify. Albinism can reduce the survivability of an animal; for example, it has been suggested that albino alligators have an average survival span of only 24 hours due to the lack of protection from UV radiation and their lack of camouflage to avoid predators. It is a common misconception that all albino animals have characteristic pink or red eyes, however this is not the case for some forms of albinism. Familiar albino animals include in-bred strains of laboratory animals, but populations of naturally occurring albino animals exist in the wild, e.g. Mexican cave tetra. Albinism is a well-recognized phenomenon in molluscs, both in the shell and in the soft parts.
context_section_description: Melanin is an organic pigment that produces most of the colour seen in mammals. Depending on how it is created, melanin comes in two colour ranges, eumelanin (producing dark browns and blacks) and pheomelanin (producing light reddish tans and blondes). The dark and light melanins have their influence either alone or in conjunction, making either plain or multi-coloured coats.  Sometimes, in a condition called agouti, they make multi-coloured individual hairs.  The production of melanin occurs in melanocytes in a complex process involving the enzyme tyrosinase.  Mammals have a gene that codes for the presence of tyrosinase in cells – called the TYR gene.  If this gene is altered or damaged, melanin cannot be reliably produced and the mammal becomes an albino. Besides the TYR gene, several other genes can cause albinism.  This is because other hormones and proteins are involved in melanin production, the presence of which is genetically determined. In mice, a total of 100 genes are known to affect albinism.
  All the genetic traits for albinism are recessive traits.  This means that their influence is hidden when paired with stronger traits. For the recessive albino trait to be expressed in a mammal, the offspring must inherit a recessive gene from both parents.
  Albinism occurs throughout the animal kingdom.  The condition is most commonly seen in birds, reptiles and amphibians, but more rarely seen in mammals and other taxa. It is often difficult to explain occasional occurrences, especially when only one documented incidence has occurred, such as only one albino gorilla and one albino koala. In mammals, albinism occurs once in every 10,000 births, but in birds, the rate is once in every 1,764 births.
  Some species, such as white peacocks, swans and geese, are not believed to be true albinos, as they do not have red eyes, rather, their colouration is suggested to be the expression of a white fur or feather gene, not a lack of melanin.
caption: This hedgehog has albinism due to a genetic mutation.
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