Merle (dog coat)

Merle is a genetic pattern in a dog's coat and alleles of the PMEL gene.

The allele creates mottled patches of color in a solid or piebald coat, blue or odd-colored eyes, and can affect skin pigment as well.

Associated breeds include Carea Leonés, Australian Shepherds and Catahoula Leopard Dogs.

The merle forms of brown are usually called "red" (though this is not correct; red and brown are genetically different), and black is called "blue" as lighter patches of black are formed throughout the coat and look slightly blue in color.

[1][2] Combinations such as brindle and sable merle exist, but are not typically accepted in breed standards.

The merle allele also plays a part in producing harlequin Great Danes.

[13] In January 2006, scientists at Texas A&M University announced the discovery of a mobile genetic unit called a retrotransposon, responsible for the various merle mutations in dogs.

[5] Certain modifying genes work in tandem (co-dominant expressive) with the merle alleles to create a completely different look to the pattern.

[22] The suppression of pigment cells (melanocytes) in the iris and in the stria vascularis of the cochlea (inner ear) leads to blue eyes and deafness.

An auditory-pigmentation disorder in humans, Waardenberg syndrome, reflects some of the problems associated with heterozygous and homozygous merle dogs and genetic research in dogs has been undertaken with the goal of better understanding the genetic basis of this human condition.

[23] Double merle dogs may be deaf or blind or both, and can carry ocular defects in blue or colored eyes.