Interestingly, double merles are subject to a variety of health problems, including hearing loss and vision deficiencies. Therefore, it is not recommended that breeders breed for the double merle phenotype. If you were in the business of breeding dogs, which of the following crosses would you avoid in an effort to not produce double merle puppies

Merle breeds involve the dog breed that have colorful pattern coat of the dogs and protect dogs from the health related problems. Double Merle breed can cause significant health related problems in dogs.

Let, the allele of the merle dogs be M. The two Merle dogs mating should not be done (MM * MM) because this cross will produce the dogs progeny with the double merle puppies. These puppies have different coat colors and suffers from the health related problems.