How do breeders use A and E genes to find masks?

Breeders use the A and E genetic series in tandem, along with modern DNA testing, to determine whether a dog carries the black mask trait and whether that mask will be visibly expressed in its offspring.

Here is how breeders use these two genes to “find” masks:

• The A-Series (Agouti gene): This locus determines the dog’s underlying base color pattern. For a mask to be visually noticeable, the dog must inherit the specific alleles on the A-series that produce a lighter base coat, such as the sable/fawn alleles (a 

y

 ) that create Fawn and Brindle Danes.

• The E-Series (MC1R gene): This locus is responsible for the actual presence of the mask, which researchers have identified as a dominant trait (E 

M

 ).

Because the mask is only visible on lighter coats, a dominant mask can be completely hidden on dogs with dark or heavily spotted coats, such as solid blacks, blues, merles, and harlequins. To “find” these hidden masks, breeders use DNA testing at the E locus to determine if a dark-colored dog secretly carries the dominant mask gene.

Furthermore, breeders use E-locus testing on dogs that already display a visible mask (such as a black-masked fawn) to determine whether they are homozygous for the trait. If the test reveals the dog carries two copies of the mask gene, the breeder knows with certainty that the dog will pass the mask trait to 100% of its puppies, guaranteeing a mask on the offspring regardless of the sire chosen. Alternatively, if the dog tests as heterozygous (carrying only one mask gene), the breeder may choose to pair them with a sire that is homozygous for the mask to ensure masked puppies.