What is the Double Merle Gene?

When we adopted Penny from a rescue that specializes in dogs with the double merle gene, we knew very little about the condition. We were considering adopting a deaf dog since we already use ASL at home. Little did I know about the connection between deafness and this genetic condition.

Having worked in the dog world for over a decade, I was surprised at how little I knew about the double merle gene. So, I did some research, and here’s what I’ve learned.

What Does “Merle” Mean?

To understand double merle, you first need to know what merle is. According to the American Kennel Club, “Also known as dapple, merle is characterized by irregular blotches of fur set on a lighter background of the same pigment, such as solid black on gray (blue merle) or solid brown on tan (red merle). Blue and partially blue eyes are often seen with the merle pattern.”

The gene responsible for the merle pattern is the same across all dogs, meaning it predates dog breeds.

What is a Double Merle?

A dog with two copies of the merle gene is called a double merle. Unlike single merles, double merles usually have mostly or entirely white coats with smaller pigment splotches. This loss of pigment is linked to many hereditary disorders.

Why Can’t Two Merles Breed?

Double merles occur when two merles are bred together. This results in a 25% chance of each puppy being blind, deaf, or both. For example, Penny is bilaterally deaf (deaf in both ears) and blind in one eye. Breeding two merles together is risky and often leads to significant health issues in the puppies.

Can a Double Merle Be Healthy?

While it’s possible for a double merle to be healthy, breeding them knowingly is irresponsible due to the high risk of producing deaf, blind, or both deaf and blind puppies. A study found that among double merles, 10% were unilaterally deaf and 15% were bilaterally deaf, compared to much lower percentages in single merles.

How Do I Know If My Dog is a Double Merle?

If your dog has mostly white fur with some patches, it might be a double merle. Genetic tests can confirm this. We knew Penny was a double merle because we adopted her from a rescue that specializes in them.

Are All Double Merle Dogs Blind?

Not all double merle dogs are blind, but they can experience various vision conditions. These include jagged pupils that make them sensitive to light and microphthalmia (small eye), which can range from almost normal appearance to no visible eye. Penny has these conditions, with her left eye having a jagged pupil and her right eye being malformed and non-functional.

Are Double Merle Dogs Aggressive?

Contrary to some misconceptions, double merle dogs are not inherently aggressive. Despite their disabilities, they are no more or less aggressive than other dogs. In our experience, Penny is the sweetest, gentlest dog we’ve ever had.

What Health Issues Do Double Merles Have?

Double merle dogs are prone to sunburn and skin cancer. Our vet advised us to always use pet-friendly sunscreen on Penny’s nose.

A study on dogs with congenital hearing and vision impairments, including double merles, found that these dogs do not have more health troubles than sensory-normal dogs. They also did not exhibit more behavioral issues such as aggression or anxiety, though they were more likely to have obsessive-compulsive behaviors.

Conclusion

Understanding the double merle gene helps us better care for dogs like Penny. By being informed, we can ensure these dogs lead healthy, happy lives despite their challenges. If you’re considering adopting a double merle dog, I highly recommend reading up on their needs and challenges to provide the best care possible.