IMacBevan
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I posted this at the end of the blizzards/ leucistic thread but wasn't sure if anyone had seen it. If this needs to go back there then the powers that be, please shuffle accordingly and I apologize.
So, I pulled all my research that I used for my lecture on color morphology in reptiles and amphibians and found the following definitions:
"Leucisism - Leucistic reptiles are completely lacking in all pigmentation and usually appear completely white. Older individuals often develop dark smudgy coloration, possibly through the same process which adds dark pigmentation to tyrosinase positive albinos"
- from VMSHerp.com.
I don't necessarily concur with their statement regarding T+ amels, my research indicates something else.
"Leucisism, also caused by an autosomal recessive gene mutation, is an inheritable defect affecting all chromatophores. Leucistic animals lack functional malanophores and xanthophores, and posess minimal iridophores. Leucistic individuals are solid white, with no pattern, except for the eyes, which are dark blue or black. Dark pigmentation is sometimes found about the body of leucistic animals, but again, melanophores are non-functional in such individuals."
- unfortunately, for some reason I didn't notate where this source was from.
These are the primary definitions that I use to quantify blizzards as leucistics.
"Leucism is a condition characterized by reduced pigmentation in animals.
Leucism is a general term for the phenotype resulting from defects in pigment cell differentiation and/or migration from the neural crest to skin, hair or feathers during 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.
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 for. Albinism results in the reduction of melanin production only, though the melanocyte (or melanophore) is still present. Thus in species that have other pigment cell-types, for example xanthophores, albinos will not be entirely white instead displaying a pale yellow colour.
More common that a complete absence of pigment cells is localized or incomplete hypopigmentism, 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 horses, the urban crow[1] and the ball python[2] 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 the retinal pigmented epithelium (RPE), 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.
Genes that, when mutated, can cause leucism include, c-kit [3], mitf [4] and ednrb [5]"
- from Wikipedia
I just found this definition on Wikipedia, so I am still absorbing what it is saying. The logic involved with it being a result of an issue during diferentian at the neural crest makes some sense to me, but I need to stew on it a bit more.
Any thoughts? Comments?
Ian B.
So, I pulled all my research that I used for my lecture on color morphology in reptiles and amphibians and found the following definitions:
"Leucisism - Leucistic reptiles are completely lacking in all pigmentation and usually appear completely white. Older individuals often develop dark smudgy coloration, possibly through the same process which adds dark pigmentation to tyrosinase positive albinos"
- from VMSHerp.com.
I don't necessarily concur with their statement regarding T+ amels, my research indicates something else.
"Leucisism, also caused by an autosomal recessive gene mutation, is an inheritable defect affecting all chromatophores. Leucistic animals lack functional malanophores and xanthophores, and posess minimal iridophores. Leucistic individuals are solid white, with no pattern, except for the eyes, which are dark blue or black. Dark pigmentation is sometimes found about the body of leucistic animals, but again, melanophores are non-functional in such individuals."
- unfortunately, for some reason I didn't notate where this source was from.
These are the primary definitions that I use to quantify blizzards as leucistics.
"Leucism is a condition characterized by reduced pigmentation in animals.
Leucism is a general term for the phenotype resulting from defects in pigment cell differentiation and/or migration from the neural crest to skin, hair or feathers during 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.
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 for. Albinism results in the reduction of melanin production only, though the melanocyte (or melanophore) is still present. Thus in species that have other pigment cell-types, for example xanthophores, albinos will not be entirely white instead displaying a pale yellow colour.
More common that a complete absence of pigment cells is localized or incomplete hypopigmentism, 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 horses, the urban crow[1] and the ball python[2] 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 the retinal pigmented epithelium (RPE), 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.
Genes that, when mutated, can cause leucism include, c-kit [3], mitf [4] and ednrb [5]"
- from Wikipedia
I just found this definition on Wikipedia, so I am still absorbing what it is saying. The logic involved with it being a result of an issue during diferentian at the neural crest makes some sense to me, but I need to stew on it a bit more.
Any thoughts? Comments?
Ian B.
Last edited:
:main_laugh: