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Leucism in Animals

Tanmay Tikekar
Many of us know about albinism, but very few are familiar with the related condition of leucism. AnimalSake explains leucism.

'Luke-ism' or 'Lucy-ism'?

Like most Latin 'C's, the 'c' in leucism is a hard C, and is pronounced as a 'k'.
Leucism, also spelled as leukism, is a condition caused by the expression of a recessive gene. The genes primarily responsible for leucism are the c-kit gene and the mitf gene. During the embryonic state, these genes produce a defective transmembrane protein which results in a lack of melanocytes or cells capable of making pigment. As a result, the animal exhibits white coat color or patches over the body.
Generally, leucistic animals retain some part of their normal pigmentation, and partial expression of leucism can be exhibited in the form of an animal having spotted or piebald appearance. The skin appears pink, its coat or fur color may vary from blond to beige to pure white.
In the animal world though, leucism tends to be disadvantageous, since the animal loses the advantage of camouflage that markings on the skin or colored coat present. Leucism is often confused with albinism, but there are significant differences between the two.

How are Albinism And Leucism Different?

Both albinism and leucism are genetic conditions caused by the expression of recessive alleles, and both terms are derived from ancient synonyms for 'white'. But while albinism is a reduction, or in most cases, the absence of the pigment melanin, resulting in an unnaturally fair complexion, leucism is a reduction or absence of all skin pigments. Albinism results in a very faint skin tone, whereas, leucism results in large patches of completely white skin and hair amidst a normally colored
► Albinism is caused in the progeny of two parents carrying the recessive gene responsible for the trait. Leucism, on the other hand, can also be caused by defects or abnormalities during the developmental stage of the fetus. Leucism is not a specific condition, but is an umbrella term of sorts for various related genetic combinations, all of which result in the same appearance.
► Another important difference between the two is the eye color. Albino animals lack the pigment necessary to determine an iris color, and thus, have pink eyes due to the visible blood vessels in the eye. On the other hand, leucistic animals have normally-colored eyes, since the pigment cells in the eyes develop independently of skin pigment cells.

Not all cases of an animal being born unusually fair are related to albinism or leucism.
A piebald animal, such as a horse, has randomly placed patches of white skin on an otherwise normally colored body. Its iris is normally colored. This makes it leucistic.

If it had been albino, there would have been no black patches, and the skin would have been of a uniform, faint color.
White tigers are neither albino or leucistic. If they were albino, their eyes would have been red. On the other hand, if they were leucistic, their stripes would not have followed the pattern seen in other, normally-colored tigers.
There are true albino tigers, but white tigers are, more often than not, a genetic variation, rather than the expression of a recessive allele. Leucistic tigers are very rare, and unseen (if not nonexistent) in the wild.
This is a case of true albinism. This Burmese python is not completely white, since only the production of melanin is hampered. If it had been leucistic, black and brown patches would have been present on its skin. Moreover, its iris (not pupil) appears red, since the blood vessels behind its eye are visible.
Leucism is most often seen in horses, cattle, cats, and crows. Offspring in the same generation, or different generations of the same bloodline, may carry randomly varying amounts of piebald complexion.