Leucism

Leucism (/ˈluːsɪzəm, -kɪz-/)[2][3][4] is a wide variety of conditions that result in partial loss of pigmentation in an animal—causing white, pale, or patchy coloration of the skin, hair, feathers, scales, or cuticles, but not the eyes.

[5] Leucism is often used to describe the phenotype that results from defects in pigment cell differentiation and/or migration from the neural crest to skin, hair, or feathers during development.

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 coloring and patterning.

This partial leucism is known as a "pied" or "piebald" effect; and the ratio of white to normal-colured skin can vary considerably not only between generations, but between different offspring from the same parents, and even between members of the same litter.

The neural crest disorders that cause leucism do not result in pink pupils and therefore most leucistic animals have normally colored eyes.

Leucistic white lions owe their colouring to a recessive allele. Note the eyes and lips remain the normal colour. Studies have shown that the reduced pigment comes from a mutation in the gene for tyrosinase , the same as causes Type I oculocutaneous albinism in humans. [ 1 ]
All-white dominant white horse with pink skin, brown eyes, and white hooves.
This white horse owes its coloring to a dominant allele ( dominant white ).
A leucistic rock dove . Both the eyes and legs are still of the normal colour.
(video) A white tiger at Tobu Zoo, in Saitama , Japan . This phenotype is due to a mutation in the same gene that results in Type IV oculocutaneous albinism in humans. [ 6 ]