What causes the ‘black mask’ trait in brindles and fawns?

The “black mask” trait commonly seen in fawn and brindle Great Danes is caused by a specific genetic variant at the E locus, which researchers have identified as the melanocortin receptor 1 (MC1R) gene.

Specifically, the mask is produced by the dominant masking allele (E 

M

 ). Because this trait is dominant, a dog only needs to inherit one copy of the E 

M

  allele to express a black mask.

While this mask is easily visible on lighter-colored dogs like fawns and brindles, the dominant mask trait can actually be inherited by dogs of any coat color. In dogs with solid black, blue, merle, or harlequin coats, the mask is still genetically present but remains visually hidden by the dog’s dark base coloring or heavy spotting. Today, breeders can use DNA testing to determine if a dog is homozygous for the masking trait (carrying two copies of the E 

M

  allele), which guarantees that the dog will pass the mask to all of its puppies, regardless of the sire chosen.