An English Mastiff, showing an extensive melanistic mask.

A New Guinea Singing Dog, showing a slight melanistic mask.

A Dogue de Bordeaux, showing a red mask which is hard to distinguish on a red coat.

The melanistic mask, often called the black mask although it may be brown (red) or gray (blue), is a pattern found in the coat of many breeds of dog, in which the hairs of at least the end of the muzzle, and frequently further up the face and into the ears, carry dark pigment. It is normal for a melanistic mask to become gray in an elderly dog.

[edit] Genetic Basis

The gene responsble encodes the Melanocortin 1 receptor protein (MC1R). It has three known alleles: E, which permits an all back coat if other genes also permit this, e, which excludes black pigment from the coat when this recessive gene is homozygous, and E^M, which causes the melanistic mask if other genes permit it. The dark pigment is eumelanin.^[1] The brindle gene is no longer thought to be at this locus.

[edit] References

1. ^ "MClR Studies in Dogs With Melanistic Mask or Brindle Patterns", S. M. Schmutz, T. G. Berryere, N. M. Ellinwood, J. A. Kerns, AND G. S. Barsh, Journal of Heredity 2003:94(1):69–73