Everything You Need to Know About Merle Dogs: Breeds, Genetics, and Health Concerns

It wasn’t too long ago that the beautiful, marbled, merle color pattern in dogs was limited to only a few dog breeds. There were dapple Dachshunds, blue and red merle herding dogs, and harlequin Great Danes. 

But over the past 10 years, this pattern has been bred into many more purebred and designer mixed-breed dogs, which has trickled down into the general mixed-breed population as well. Unfortunately, when two merle colored dogs are bred, there is a 25 percent chance that each puppy will receive the dominant merle gene from each parent. This is called double merle, which is linked to serious congenital ear and eye defects. Here’s what you need to know about merle dogs and puppies.

What is a merle?

Merle is a color pattern in dogs characterized by marbling of lighter, dilute colors on top of a solid background. The pattern is random but can appear in small patches or more extensively, sometimes covering the whole dog. 

Blue merle refers to black and gray marbling. Other merle coloring includes red merle, fawn merle, and chocolate merle. Some dogs can have a mix of merle colorings. 

Although blue eyes are very common in merle dogs, eye color can vary between blue, green, and brown, with some dogs having two different-colored eyes. The nose of a merle-patterned dog can be pink, black, or pink and black.

What gene causes merle in dogs’ coats?

The genetics behind merle color patterns are quite complicated, with many factors influencing the intensity of color, including breed and genetic variations. Here’s a brief explanation of how merle genes work.

First, a quick science refresher: Recessive genes are written in lowercase letters, while dominant ones get uppercase ones. In the case of dogs, the dominant merle gene, commonly designated with a capital M, dictates their color pattern. 

• Solid color dogs have two recessive color-pattern genes, designated as mm. 

• Merle-colored dogs have one solid and one merle gene, indicated as Mm. 

When a solid-colored dog, mm, is bred with another solid-colored dog, mm, there is a 100 percent chance that all puppies will be solid. And when a solid colored dog, mm, is bred with a merle colored dog, Mm, the outcome is 50 percent solid (mm) and 50 percent merle (Mm).

The problem with double merle

So what happens when a merle colored dog (Mm) is bred with another merle dog (also Mm)? 

There is a 25 percent chance each puppy will be solid (mm), a 50 percent chance each puppy will be merle (Mm), and a 25 percent chance that each puppy will receive two dominant merle genes (MM), which is called double merle.

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Unfortunately, although double merle is linked to a beautiful white haircoat with scattered merle patches, blue eyes, and a pink nose, it is also linked to congenital ear and eye defects, affecting a dog’s vision and hearing. Hearing loss is directly related to the lack of pigment in the inner ear.

Phantom merle genes

Ethical breeders know to avoid breeding two merle colored dogs together, but sometimes merle dogs aren’t easy to identify. Phantom merle dogs may carry the gene without showing typical merle patterning.

Phantom merles are generally red dogs, where dilution of the lighter colors of the merle pattern makes it look like they have a solid coat. This is why DNA testing is crucial when breeding dogs who could carry the merle gene, to prevent unintentional double-merle pairings. 

De souza / Pexels/ Double merle Aussie dog

Popularity leads to poor breeding practices

The major issue with breeding merle dogs arises when, rather than safely breeding a solid-colored dog to a merle dog, two merle dogs are either intentionally or accidentally bred. 

Merle-to-merle breeding can occur when unethical breeders risk producing double-merle puppies to create very splashy-looking coats. They might discard disabled double-merle puppies or send them to rescue organizations. Some sell double merles as exotic dogs to unsuspecting customers, who may then either choose to keep the potentially deaf/blind puppy, return them, or rehome them.  

Some backyard breeders and families are unaware of the potential risks when breeding two merle dogs. They learn after the fact, when the litter includes double merles with congenital ear and eye defects. Finding homes for these disabled puppies isn’t always easy. 

Thankfully, there are many resources available to pet parents who choose to adopt a double merle. 

Health implications of merle breeding

The most common health problems linked to double-merle breeding are vision and hearing issues. Most double-merle dogs are partially or fully deaf and/or blind, with a wide variation in outcomes. (A small number of double merles can see and hear.) Double-merle dogs carry an increased risk of secondary health issues. Here are a few you can expect.

• Eye abnormalities may include starburst pupils, iris abnormalities, microphthalmia (small eyeballs), and/or corectopia (eyes pointing downward or to the side). 

• Secondary consequences to eye defects include uveitis, glaucoma, retinal detachment, and the need for enucleation. 

• Double-merle eye changes are similar to Collie eye anomaly. These changes can be mild to severe, and may cause congenital blindness or blindness later in life.

• Studies have found that partial or total hearing loss occurs in at least 25 percent of double merles.

• Their blue eyes are sensitive to the sun, and they tend to have increased anxiety due to hearing and vision issues. 

• Since double merles tend to be light-skinned with a pink nose, they’re more prone to sunburn, which can increase the risk of secondary skin cancer. 

Before you adopt a merle dog, inquire about the pup and their needs to make sure you can properly care for them. Make sure a shelter or rescue informs you about any known health issues, and after adoption, book a vet checkup to catch health issues early.

Caring for double merle dogs, especially those who are hearing and vision impaired, requires a little extra dedication and making safety a priority. But most of these dogs will adapt and lead very happy lives.

Merle dog breeds

Merle shows up in quite a few purebred and mixed-breed dogs. (That said, merle color patterns are not recognized in all breeds by the American Kennel Club and other kennel clubs.) Below are a few breeds in which you might see merle coats.

This list doesn’t include all the Doodle mixes, Chihuahua mixes, and countless other “designer” dogs being bred irresponsibly. Adding merle coloring to any breed increases the potential for merle-related health issues, compounding concurrent breed-related heritable conditions.

Andrea / AdobeStock/

1.  Australian Shepherd

Aussies are a high-energy breed who do best with active families and plenty of mental stimulation. Both the Aussie and the smaller Mini Australian Shepherd have coats that can be merle, blue, or red — and those patterns are part of the breed standard. They’re generally healthy, but can be prone to hip dysplasia and certain eye issues, especially in merle-to-merle pairings.

Traits

• Height: 18 to 23 inches

• Weight: 38 to 66 pounds

• Merle pattern: Breed standard

kathrineva20 / AdobeStock/

2. Border Collie

Border Collies are another high-energy herding breed who needs as much mental stimulation as physical exercise. The classic Border Collie is black and white, but there are many varieties of color patterns (including merle) and hair-coat length. They tend to be healthy dogs, but there is an increased incidence of hip dysplasia, Collie eye anomaly, PRA, and hearing impairment, especially in double merle Border Collies. 

Traits

• Height: 18 to 21 inches

• Weight: 31 to 53 pounds

• Merle pattern: Breed standard

Lidia / AdobeStock/

3. Catahoula Leopard Dog

Catahoula Leopard Dogs are versatile herding and working dogs. They are very athletic, so they do well in canine agility. Their distinct look is due to a wide range of colors and patterns. Unfortunately, there are many beautiful Catahoula dogs in need of homes due to overbreeding and mixed breeding, especially in the southern regions of the US. Health issues include hip dysplasia, congenital deafness, and eye diseases.

Traits

• Height: 20 to 26 inches

• Weight: 45 to 87 pounds

• Merle pattern: Breed standard

Peter Jochim Pema / Pexels/

4. Dachshund

Dachshunds are known for their hot dog shape: long backs and short legs. (This comes with a high incidence of intervertebral disc disease, or IVDD.) The Dachshund merle pattern is often referred to as “dapple,” and can be seen in all three haircoat types (short, long, and wired hair), as well as in the breed’s miniature and standard sizes. With dapple being so popular, unfortunately, there is an abundance of double-dapple Dachshunds in need of homes.

Traits

• Height: 8 to 11 inches

• Weight: 16 to 32 pounds

• Merle pattern: Breed standard

Ayehab / AdobeStock/

5. American Pit Bull Terrier

Pit Bulls have huge fan bases, but are also often the target of breed-specific legislation (BSL). In general, Pit Bulls and Pit mixes are healthy, but they come with an increased risk of orthopedic problems (such as hip dysplasia and ACLs), as well as hearing impairments. Irresponsibly breeding merle into Pit Bulls increases the risk of double-merle puppies.

Traits

• Height: 17 to 22 inches

• Weight: 30 to 66 pounds

• Merle pattern: Recently introduced

Volodymyr Dobrovolskyy / Unsplash/

6. Cardigan Welsh Corgi

Corgi dogs are a compact herding breed who can be red, sable, or black and white, as well as brindle or merle and white. Health issues seen in Corgis include hip dysplasia, cataracts, PRA, and degenerative myelopathy.

Traits

• Height: 10 to 13 inches

• Weight: 23 to 42 pounds

• Merle pattern: Breed standard

efrem efre / Pexels/

7. Great Dane

Great Danes are a giant breed weighing upwards of 200 pounds. Coats are short with solid black, blue, fawn, brindle, harlequin, mantle, or merle. Health issues include bone and other cancers, heart disease, and several orthopedic issues.

Traits

• Height: 29 to 35 inches

• Weight: 95 to 153 pounds

• Merle pattern: Breed standard

big world in alens / Pexels/

8. Chihuahua

Chihuahuas are tiny but mighty, with big personalities. This popular breed comes in many color combinations. Although not accepted in the breed standard, merle coloring has been brought to the Chihuahua breed, creating the potential for double merle Chihuahuas. They are overall healthy, but can be born with a number of congenital limb deformities or missing limbs. 

Traits

• Height: 6 to 9 inches

• Weight: 2 to 9 pounds

• Merle pattern: Recently introduced

Julissa Helmuth / Pexels/

9. Pomeranian

Pomeranians are fluffy little lap dogs. They are very sweet and a little yappy. Daily play and mental stimulation are a must, even if their exercise needs aren’t huge. Health issues include collapsing trachea and luxating patellas. They come in solid colors as well as merle.

Traits

• Height: 7 to 12 inches

• Weight: 3 to 10 pounds

• Merle pattern: Breed standard

gundula vogel / Pexels/

10. French Bulldog

Frenchies are low-energy companion dogs. Merle patterns introduced to this breed come from questionable breeding, and prospective pet parents should know the brachycephalic breed is prone to serious health issues, especially with breathing and spine development.

Traits

• Height: 12 to 13 inches

• Weight: 19 to 34 pounds

• Merle pattern: Recently introduced

Paws It Forward Dog Rescue Society/

11. Cocker Spaniel

Cocker Spaniels are another breed who has been brought into the world of merle coloring. The Cocker Spaniel has always been a popular breed due to their medium size, happy personality, and adorable floppy ears. Although these ears are very cute, they are also a source of chronic infections. Other health issues include cataracts, glaucoma, hip dysplasia, and allergies.

Traits

• Height: 15 to 16 inches

• Weight: 23 to 41 pounds

• Merle pattern: Recently introduced

Looking for a merle? Start with adoption

As with any dog, purebred or mixed-breed merle colored dogs can be found in rescues and shelters across the US. As beautiful and desirable as they might be, they are still dogs. People buy and adopt dogs who don’t match their lifestyles, and these dogs find themselves homeless. 

Because there are so many breeds and breed mixes who have merle coloring, you are sure to find what you are looking for at your local shelter or rescue group. You can start your search with Adopt a Pet, which lets you search by location, breed, age, and many other criteria.

Commonly asked questions

What is a double-merle dog?

A double-merle dog comes from breeding two merle-colored dogs. When two merle-colored dogs (purebred or mix) are bred together, there is a 25 percent chance that each puppy will receive a dominant merle gene from each parent. When this happens, the puppy is double merle (or has two merle genes). Double-merle dogs tend to have a white or mostly white haircoat, pink or partly pink nose, blue eyes — but they may also be born with congenital ear and eye defects, which can include partial or complete hearing and vision loss. 

What breeds does merle naturally occur in?

Merle coloring was originally found in herding breeds, Dachshunds, and Great Danes. Because merle coloring is beautiful and desirable, the color pattern has more recently been bred into both purebred and mixed-breed designer dogs. Unfortunately, as merle dogs are bred to produce cool, flashy-colored puppies, the potential for more double-merle, disabled puppies increases dramatically. 

Why can’t two merles breed?

Two merles can theoretically breed, but when they do, there is a 25 percent their puppies will be double merle, which is linked to congenital ear and eye defects. 

How common is the merle coat color in French Bulldogs?

Merle coat color is uncommon in French Bulldogs, but not unheard of. This brachycephalic breed of dog already has a long list of health issues, so adding the potential for double merle breeding into the mix is very unfortunate for the breed. 

Is it normal for a merle dog’s coat to change color?

Yes, this is normal: As a dog ages, their merle coat color will change to a lighter color due to graying. 

Is the merle gene bad?

The merle gene is not inherently bad, provided people are responsible in the way they breed merle-colored dogs. Of course, there are many rescued merle-colored dogs waiting to be adopted. 

Are merle dogs unhealthy?

No, merle dogs are not inherently unhealthy. Merle dogs’ health tends to align with their breed and family lines. For example, herding breeds, whether merle or solid, have a higher occurrence of Collie eye anomaly and multidrug resistance 1 (MDR1) sensitivity, which can be identified through DNA testing. 

References

‌Dockweiler, Jenna, and Aly Cohen. “Drug Sensitivity: MDR1.” Cornell University College of Veterinary Medicine, 9 Aug. 2022, www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-information/drug-sensitivity-mdr1.

‌“Dog Coat Colour Genetics.” Doggenetics.co.uk, 2025, www.doggenetics.co.uk/merle.html. Accessed 24 July 2025.

‌“Merle | Veterinary Genetics Laboratory.” Vgl.ucdavis.edu, vgl.ucdavis.edu/test/merle.

Shapiro, Melissa. “Causes of Hearing and Vision Loss Together.” Disabled Pets, Piglet International Inc., www.disabledpets.org/pdf/Deaf-Blind-Pets.pdf.