A merle Great Dane is a dog of the Great Dane breed that has a mottled coat consisting of a gray or light-cream background and small black spots. Merle Great Danes are often produced when breeding for harlequin-coat Great Danes, dogs that have black spots on white fur.
Although the genetics for merle are associated with the genetics for harlequin patterned dogs, harlequin is a recognized coat pattern for the breed, while merle is not. This is to discourage the breeding of merle dogs, because dogs that are the product of two merle parents are often stillborn, or they are born deaf and blind. The merle gene affects the production of melanin, a molecule responsible for pigmentation, sight and hearing. Dogs that receive one copy of the gene from each parent are homozygous for merle. They have no healthy genes to compensate for the effects, so they develop congenital abnormalities.