Australian Shepherd: The most common merle breed, with over 1/3 of Aussies sporting the distinctive coat pattern. They come in blue merle and red merle.
Border Collie: While not as common as Aussies, merle Border Collies do exist. They typically have the classic black and white coat, but can also be found in pure black, red, sable, brindle, red merle, and blue merle.
Cardigan Welsh Corgi: The only Corgi type with the merle gene. These short-legged cuties are most commonly found in blue merle, with red merle being extremely rare.
Catahoula Leopard Dog: Named for their spotted merle coat, they come in blue or red merle and can also have solid colors. Some have heterochromia, with each eye a different color.
Chihuahua: Not a naturally occurring Chihuahua color, merle was bred into the breed. Ethical breeders avoid breeding merle Chihuahuas due to potential health problems with hearing and sight.
Collie: Both rough and smooth Collies can have the merle gene, giving their long fur a striking mottled pattern. They are typically found in a blue merle that appears light or dark grey.
Dachshund: Merle Dachshunds are called "dapple" Dachshunds. They have the same cute patchy pattern, but are unfortunately prone to more health issues than other Doxies due to the merle gene.