A Cavalier King Charles Spaniel exhibiting the blue merle color pattern presents a unique and relatively rare variation within the breed. This coat coloration is characterized by patches of diluted black pigment, resulting in a mottled or marbled appearance, set against areas of undiluted black or tan. The presence of merle is determined by a specific gene that affects the distribution of pigment in the coat, eyes, and sometimes skin. It is important to recognize that the standard for the Cavalier King Charles Spaniel breed typically describes four accepted colors: Blenheim, Tricolour, Ruby, and Black and Tan. The blue merle pattern, while visually striking, falls outside these traditionally recognized standards.
The emergence of this color variation within the Cavalier King Charles Spaniel lineage is attributed to crossbreeding with other breeds carrying the merle gene. Understanding the genetic basis of the merle pattern is crucial for breeders. Merle is a dominant trait; therefore, only one copy of the merle allele is necessary for it to be expressed. However, breeding two merle dogs together carries a significant risk of producing puppies with serious health issues, including deafness and blindness, due to the potential for homozygosity for the merle allele (MM). Responsible breeders prioritize genetic testing and careful selection to avoid these health complications.
