Leucism
2404069
213227496
2008-05-18T11:34:46Z
B.d.mills
67403
+picture of white lion
[[Image:White Lion.jpg|thumb|right|[[White lion]]s owe their coloring to a recessive gene.]]
'''Leucism''' is a condition characterized by reduced [[pigmentation]] in animals. Unlike [[albinism]], it is caused by a reduction in all types of skin pigment, not just [[melanin]].
Leucism is a general term for the [[phenotype]] resulting from defects in [[chromatophore|pigment cell]] differentiation and/or migration from the [[neural crest]] to skin, hair or feathers during [[morphogenesis|development]]. This results in either the entire surface (if all pigment cells fail to develop) or patches of body surface (if only a subset are defective) having a lack of cells capable of making [[pigment, biology|pigment]].
Since all pigment cell-types differentiate from the same [[multipotent]] precursor cell-type, leucism can cause the reduction in all types of pigment. This is in contrast to albinism, for which leucism is often mistaken. Albinism results in the reduction of [[melanin]] production only, though the [[melanocyte]] (or [[Chromatophore#Melanophores|melanophore]]) is still present. Thus in species that have other pigment cell-types, for example [[Chromatophore#Xanthophores_and_erythrophores|xanthophores]], albinos are not entirely white, but instead display a pale yellow colour.
More common than a complete absence of pigment cells is localized or incomplete [[hypopigmentation]], resulting in irregular patches of white on an animal that otherwise has normal colouring and patterning. This partial leucism is known as a "pied" or "[[piebald]]" effect; and the ratio of white to normal-coloured skin can vary considerably not only between generations, but between different offspring from the same parents, and even between members of the same litter. This is notable in [[horse]]s, the urban [[crow]]<sup>[http://www.birds.cornell.edu/crows/whitecrows.htm]</sup> and the [[ball python]]<sup>[http://www.constrictors.com/Collection/BallPythons/PiebaldBallPython.html]</sup> but is also found in many other species. In contrast, albinism always affects the entire animal.
A further difference between albinism and leucism is in [[eye colour]]. Due to the lack of melanin production in both the [[retina]]l pigmented epithelium (RPE) and [[iris (anatomy)|iris]], albinos typically have red eyes due to the underlying blood vessels showing through. In contrast, leucistic animals have normally coloured eyes. This is because the melanocytes of the RPE are not derived from the neural crest, instead an outpouching of the [[neural tube]] generates the [[optic cup]] which, in turn, forms the [[retina]]. As these cells are from an independent developmental origin, they are typically unaffected by the genetic cause of leucism.
[[Gene]]s that, when [[mutated]], can cause leucism include, ''[[c-kit]]'' [http://omia.angis.org.au/retrieve.shtml?pid=2192], ''[[Microphthalmia|mitf]]'' [http://hmg.oxfordjournals.org/cgi/content/abstract/8/8/1431] and ''[[ednrb]] [http://www.infobiogen.fr/services/chromcancer/Kprones/WaardenburgID10089.html]
==Term origin and pronunciation==
The terms ''leucistic'' and ''leucism'' are derived from [[medical terminology]]. The [[prefix]] ''leuc-'' is the [[Latin]] variant of ''leuk-'' from the [[Greek language|Greek]] ''leukos'' meaning "white" (see Steadman’s, Dorland’s or Taber’s medical dictionaries). The correct pronunciation of ''leucistic'' is (''loo-kiss-tic'') and ''leucism'' is (''loo-kism'') since the prefix in Greek and Latin are pronounced with the hard C or K sound. Since the prefix ''leuc-'' is a variant of ''leuk-'', in medical circles the terms may also be spelled with a k (''leukistic'' and ''leukism'').
==Gallery==
<gallery>
Image:Leucistic_Texas_Rat_Snake.jpg|Leucistic Texas Rat Snake (''[[Elaphe obsoleta]]'')
Image:Common_Grackle_Leucistic.jpg|Leucistic Common Grackle (''[[Quiscalus quiscula]]'')
Image:Baillsundfuggel.JPG|Leucistic Indian Peafowl (''[[Pavo cristatus]]'')
Image:ChippingSparrow.jpg|Leucistic Chipping sparrow (''[[Spizella passerina]]'')
Image:Long finned oscar.jpg|Leucistic Long Finned Oscar (''[[Astronotus ocellatus]]'').
</gallery>
==See also==
* [[Vitiligo]]
* [[Albinism]]
* [[Melanism]]
[[Category:Pigment disorders]]
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