More Info

Did you know?

All Merle dogs are thought to have descended from a single Collie-type dog with the variant, that lived in Britain before 1870. Merle primarily affects dark pigment appearance, so in red dogs, the coat color mottling with be subtle. In the Catahoula Leopard Dog breed in which merle is common, blue eyes are called "glass eyes" and when partially blue, are called "cracked" eyes. The merle variant length can vary, and impacts whether the standard Merle pattern is seen. Occasionally, the merle variant can be elongated, called harlequin merle. This is a different gene than the Harlequin variant seen in the Great Dane.

How it works

Most dogs with one copy of the Merle variant will show Merle patterning. Most dogs with two copies will be mostly white, but in some cases will show Merle patterning. Some dogs with this variant will not show the Merle pattern. This is because the Merle variant can sometimes be shortened (known as cryptic or atypical Merle), and these forms do not have an effect on appearance.

Health implications

A dog that inherits two copies of merle is called a "double merle" and, unless atypical or cryptic merle variants are present, this poses a significant health risk to the dog. Double merle dogs are often deaf and blind at birth, and may also have abnormally small eyes (microphthalmia). For this reason, two visibly merle dogs should never be bred together.