If you've heard of a harlequin Great Dane, but never a harlequin of any other dog breed, there's a reason. The harlequin pattern is exclusive to Great Danes, although that wasn't always the case. Other breeds, such as the miniature pinscher, once exhibited this gene-related coloration, but it was considered undesirable and not permitted in registered dogs.
A harlequin pattern consists of a white primary color with scattered patches of black. Blue patches sometimes appear in the great Dane, but that's not a desirable shade in the breed. Merle patterns, common in various dog breeds, are related to the harlequin. No two harlequin Great Danes possess the exact same coat pattern.
Merle patterns not only appear in dogs, but in equines and other species. Also referred to as dappling, merle isn't a color, but darker shades of pigment on a light base coat. Dogs inheriting the merle gene also might inherit a merle modifier, which determines the merle pattern. If a Great Dane inherits a merle gene but not a harlequin gene, he won't have the harlequin coat pattern.
The Great Dane Club of America reports that researchers at South Carolina's Clemson University discovered the gene causing the harlequin phenotype -- or the obvious coloring in a dog. The harlequin gene does not produce pigment. Rather, according to the researchers, it alters the merle gene's effects. The diluted areas of merle coloring usually seen are predominately removed from the hair pattern, resulting in the bi-color harlequin.
Color genes don't just affect the dog's coat, but are linked to certain health issues. Predominately white harlequin Great Danes usually have two merle genes. These dogs are far more likely to suffer from deafness and vision problems than Danes of other hues. Microphthalmia, a condition causing unusually small eyes recessed into the eye socket also affects these dogs. Great Danes with two merle genes are also prone to neurological, reproductive and immune system issues.
Breeders interested in whether their Great Dane carries the harlequin gene, even if the dog does not have the color pattern, can order genetic tests for coat color. Send the genetic company a sample of your dog's DNA by swabbing his cheek. Breeders can avoid potential genetic issues by avoiding breeding Danes with the merle gene to another dog with the gene.