Can a dog carry Harlequin without showing it?

Yes, a dog can carry the Harlequin gene without visibly showing it.

This occurs when a dog inherits the Harlequin gene but does not inherit the Merle gene. Because the Harlequin gene acts specifically as a modifier to the Merle pattern, it requires the presence of the Merle gene to be visually expressed.

If a dog lacks the Merle gene (possessing the mm or wild-type genotype), the Harlequin gene has no visible effect on their appearance, and the dog will simply have a normal coat color, such as solid black or mantle. Dogs with red pigment only also cannot express the Harlequin gene.

Breeders refer to these non-merle dogs as “carrying” Harlequin because they can still pass the hidden gene on to their offspring. For example, a solid black Great Dane that carries Harlequin can be bred with a merle dog and successfully produce Harlequin puppies.