Merle is a coat pattern found in Australian Shepherds, Collies, Shelties, and a number of other dog breeds. This particular phenotype is inherited as an autosomal, incompletely dominant trait. The merle gene creates mottled patches of color in a solid or piebald coat, blue or odd-colored eyes, and affects skin pigment.
Animals that are “double merle,” a common term used for dogs that are homozygous (having two copies) of the merle (M/M) trait, are predominantly white and prone to several health issues. The chances of having puppies that develop health issues increase when two Merles are bred together. It is recommended that a Merle dog only be bred to a non-merle/non-cryptic Merle dog. Cryptic merle dogs do not appear to be merle, but contain the merle gene. Many solid dogs are actually cryptic, also known as phantom, merles and can produce both merle and double merles if not careful.
Merle can affect all coat colors. Recessive red dogs can also be affected by Merle, but the patches are either hardly seen or (if the dog is a clear recessive red) are not visible at all. Combinations such as brindle Merle exist, but are not typically accepted in breed standards.
In addition to altering base coat color, Merle also modifies eye color and the coloring of the nose and paw pads. The Merle gene modifies the dark pigment in the eyes, occasionally changing dark eyes to blue, or only part of the eye to blue. Since Merle causes random modifications, both dark-eyed, blue-eyed, and odd-colored eyes are possible. Color on paw pads and nose may be mottled pink and black.
Clark LA, Wahl JM, Rees CA, Murphy KE. Retrotransposon insertion in SILV is responsible for merle patterning of the domestic dog. Proc Natl Acad Sci USA. 2006 Jan 31; 103(5):1376-81. [PubMed: 16407134]
Kaelin CB, Barsh GS. Genetics of pigmentation in dogs and cats. Annu. Rev. Anim. Biosci. 1:16.1-16.32 (2013).
|M/M||Homozygous: Dog has two copies of the merle allele and will display a maximal merle pattern. The gene will be passed on to every offspring.|
|M/Ma||Dog has one copy of the merle allele and one copy of the atypical merle allele.|
|M/Mc||Dog has one copy of the merle allele and one copy of the cryptic merle allele|
|Ma/Ma||Dog has two copies of the atypical merle allele, and will likely display minimal merle patterning.|
|Ma/Mc||Dog has one copy of the atypical merle allele and one copy of the cryptic merle allele.|
|Mc/Mc||Dog has two copies of the cryptic merle allele.|
|n/M||Heterozygous: Dog has one copy of the merle allele|
|n/Ma||Dog has one copy of the atypical merle allele|
|n/Mc||Dog has one copy of the cryptic merle allele.|
|n/n||Clear: Dog is negative for the mutation associated with merle.|
|NR||No Result- Please submit a new sample for this animal.|