What is a Double Merle?
First, let us explain the merle pattern in a dog's coat.
Merle is a genetic pattern that comes in different colors and patterns and can affect all coat colors. The merle gene creates mottled patches of color in a solid or piebald coat, blue or odd-colored eyes, and can affect skin pigment as well.
If two merle dogs are bred together, each puppy in the litter has a 25% chance of being born a double merle. Double merles also have a very high chance of being deaf, blind, or both because they lack pigment where it would normally be. The pups that do not inherit the gene twice do not have genetic issues.
Breeds that commonly have merle coats: