Merle (dog coat)

Merle is a distinctive coat pattern in dogs characterized by patches of diluted pigment interspersed with patches of full color. It is one of the more complex genetic traits in dogs, resulting from the interaction of multiple genes. The merle pattern is most commonly associated with the Australian Shepherd, but it can also be found in other breeds such as the Collie, Shetland Sheepdog, Dachshund, and Great Dane, among others.

Genetics

The merle coat pattern is primarily determined by the M locus, where the merle allele (M) is dominant over the non-merle allele (m). A dog with one copy of the merle allele (Mm) will typically show the merle pattern, while a dog with two copies (MM) may have extensive white areas and is often referred to as a "double merle." Double merles are associated with increased health risks, including deafness and blindness, due to the lack of pigment in the inner ear and eyes.

Health Concerns

Health concerns associated with the merle pattern are primarily seen in double merles, as the lack of pigment can affect the development of the eyes and ears. Dogs with the double merle genotype can suffer from microphthalmia, anomalies of the iris, and deafness. Breeders are advised to avoid breeding two merle-patterned dogs to prevent these health issues.

Breeds

While the merle pattern is most famously seen in the Australian Shepherd, it is not exclusive to this breed. Other breeds that can exhibit the merle pattern include:

• Collie
• Shetland Sheepdog
• Dachshund
• Great Dane
• Border Collie
• Cardigan Welsh Corgi

Each breed has its own standard for the merle pattern, and in some breeds, the pattern may be disallowed or restricted.

Controversy

The breeding of merle dogs, especially the deliberate breeding of double merles, is a subject of controversy. The potential for serious health issues in double merle dogs has led to calls for responsible breeding practices, including genetic testing and breeding restrictions to prevent the production of double merle puppies.

Conclusion

The merle coat pattern is a beautiful and complex genetic trait that requires responsible management by breeders to prevent health issues. While it is admired by many for its unique appearance, the welfare of the dogs should always be the primary concern.