Merle (coat colour in dogs)

Merle is a pattern in a dog's coat. "Merle" comes in different colors and patterns. Some have blue patches throughout and are considered blue "merle"; same with red, and chocolate, although some describe merle as only a "pattern". DNA testing identifies the "Merle" gene but not the variety of colors and patterns seen in the coats of the dogs with the gene. A dilute black (BB or Bb) dog is generally known as blue, but a dog with a merle coat does not test BB or Bb but still is a blue dilute from the "merle" gene 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. Health issues are more typical and more severe when two merles are bred together, so it is recommended that a merle be bred to a dog with a solid coat color only.

Merle can affect all coat colors. The merle forms of brown and black are usually called "red" (though this is not correct; red and merle are genetically different) and "blue" as patches of blue are formed throughout the coat. Merle is a dilution gene just like the blue, chocolate in a traditional color but without the color of blue DNA. Merle has its own colours and DNA; a blue merle is a dog who has blue patches on its body, red and some are chocolate or "cookies and cream". Dogs who are recessive red can still 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 coloring on the nose and paw pads. The merle gene modifies the dark pigment in the eyes, occasionally changing dark eyes to blue, or part of the eye to be colored blue. Since merle causes random modifications, however, both dark-eyed, blue-eyed, and odd-colored eyes are possible. Color on paw pads and nose may be mottled pink and black.

Merle is a distinguishing marking of several breeds, particularly the Alapaha Blue Blood Bulldog, Australian Shepherd, and appears in others, including the Koolie, German Coolies in Australia, the Shetland Sheepdog, various Collies, the Welsh Corgi (Cardigan), the Pyrenean Shepherd, the Bergamasco Sheepdog, the Old English Sheepdog, and Catahoula Leopard Dog. In Dachshunds the merle marking is known as "dapple". It is also present in the Pomeranian and Chihuahua, but is a disqualification according to the FCI, the Canadian Kennel Club [CKC] and other kennel club standards. It is only the American Kennel Club [AKC] that allows the registration of the 'merle.' In the Cocker Spaniel breed, it is a recognized pattern, although incorrectly listed as a 'color'. The merle gene also plays a part in producing harlequin Great Danes and Beaucerons. In several breeds, such as the Pomeranian and Chihuahua, merle is an indicator of cross breeding by many breeders and associations.

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Wikipedia