You’ve heard a dog’s color described as “merle,” but what is a merle dog?
What is a blue merle dog?
What should you know about dogs with this beautiful pattern in their coat?
Does the color affect their health?
In fact, it does. And it’s something you should know about if you love the way merle dogs look!
If you’re interested in finding out about merle dogs, and whether this should influence your choice of pet, read on!
The Origins of the Merle Color
The merle dog coat is also called a dapple pattern (depending on the breed), in which irregular patches of darker hair are laid over a lighter, or diluted, shade of the same pigment.
Merle dog breeds include Australian Shepherds, Collies, Dachshunds, Cardigan Welsh Corgis, Great Danes, and Shetland Sheepdogs.
These can be blue merle dog breeds or red merle dog breeds.
Other breeds that may show a merle color coat include:
- Border Collies
- Pyrenean Shepherds
- Catahoula Leopard Dogs
- Bergamasco Sheepdogs
- American Staffordshire Terriers (pit bulls)
- Old English Sheepdogs
- American Cocker Spaniels
- Beucerons and
In some breeds, such as the Australian Shepherd, the color is a distinguishing characteristic. In others, such as the Dachshund, merle coloration isn’t considered desirable because of the associated genetic weakness.
Merles are generally split into the blue merle dog and the red merle dog based upon the type of melanin produced.
Some breeds also show:
- fawn, and
- chocolate merle patterns.
The pattern has been in dogs for many years, but wasn’t called merle until the early 2000s.
The Genetics of The Merle Dog
The gene that causes merle in dogs is called PMEL17 or SILV.
The merle color pattern is what scientists call “incompletely dominant.”
It shows up when a dog gets just a single copy of the merle allele. It basically causes a dilution of color.
Researches have isolated three different alleles, or variants, for merle. These are the merle allele (M), the cryptic merle (Mc), and non-merle (m).
Merle dogs have one allele for merle and one for non-merle, which is expressed as Mm.
Cryptic merle refers to a pattern called phantom or ghost merle. Often, these dogs have the M genotype but don’t express it.
Cryptic merles are usually either liver or black, with some small areas of merle. Some don’t look like merles at all.
The inheritance of M and Mc is unstable. Sometimes M may produce Mc, and vice versa.
This makes merle inheritance complex. It can also cause potential health concerns.
Dogs with two copies of the M allele, called double merle (MM), tend to be white with patches of color.
If you’ve heard the term “lethal white,” it (somewhat misleadlingly) refers to the MM genotype.
What makes the merle color even more complicated is that there are modifying genes that work with the merle gene to create different phenotypes (the look of the dog based on its genes).
These include the harlequin merle, in which the “blue” is replaced with white to create a white dog with black patches.
It also includes patchwork or tweed merle, in which the “blue” or “red” becomes gray, tan, and brown. Patches in tweeds may be bigger in size, range, and dilution intensity.
Merle acts upon eye pigment in the iris as well, so a blue eyed merle dog or merle dogs with partially blue eyes are common.
Health of the Merle Dog
The merle gene is unfortunately linked with impaired function of the auditory, ophthalmologic systems, and immune systems of dogs.
That’s because color and color pattern in dogs is associated with the development of the nervous system in the dog embryo. They all come from the same cells.
The problems are caused in part by the suppression of pigment cells in the inner ear and the iris of the eye.
Merle dogs are known to be vulnerable to a wide range of defects in the eyes and ears. The blue eyes sometimes make it more difficult to diagnose eye problems, as well.
One study found that deafness affected 9.2 percent of dogs with the merle allele, with 3.5 percent in single merles and 25 percent in the double merle dog.
Other studies have found similar results, showing also that double merle (MM) dogs experience ear and eye effects at a much higher rate than single merle dogs.
There may be differences based upon breed, too. Collie-type breeds seem more affected by deafness than others.
One of the conditions merle dogs may suffer from is microphthalmia with coloboma.
This is a recessive trait that may show up in merles with a predominately amount of white hair (as with MMs), in which the eyes are abnormally small and may have anatomic malformations in the lens, iris, or retina.
Other conditions include:
- distortion of the eye’s appearance
- night blindness
- a cleft in the iris, and
- third eyelids.
Some double merle dogs have been known to be born without eyes at all.
Merle Dog Appearance
The random patches of color on top of the lighter color is unusual and distinctive, and make merle dogs’ pictures beautiful!
In blue merles, the color is mottled black atop black-and-white dilute hair. In red merles, the color is a mottled brown on top of lighter brown hair.
You’ll still see patches of undiluted pigment over the dog’s body.
The merle gene seems to affect mostly the black pigment. In a Mm dog, a tan color is not necessarily diluted. Thus, a blue merle dog may still have tan points.
MM dogs will be mostly white, with patches of color. Double merle dogs are not accepted at dog shows.
Merle Dog Temperament
The merle color gene does not have an effect on temperament, as far as researchers know.
If you are looking for a dog with this type of coloring, we recommend you learn about the temperament of the breed in question, rather than the pattern of coloring.
We can’t generalize in this respect, because the breeds that show merle coloration are all so different!
Merle Dog Intelligence
Some of the breeds that have merle coloring as one of their distinguishing characteristics are known to be quite intelligent!
However, there doesn’t seem to be any relationship between intelligence and merle coloration.
If you’re looking for a smart breed of dog, the merle coloring will not necessarily be a factor.
Merle Dog Grooming
Again, this is something that depends on the breed. Many merle dog breeds have long hair that requires a fair amount of maintenance.
Australian Shepherds, for example, have a waterproof, double-layered coat that sheds seasonally. It requires thorough weekly brushing.
On the other hand, pit bulls have a short, stiff coat that doesn’t need much care, and only sheds occasionally.
If you are looking for a merle dog, check out the breed information for its grooming requirements.
Merle Dog Training
Whatever dog you end up getting, training will be important for your pup’s overall socialization and happiness.
We recommend basic obedience and agility training for larger, active merle dogs, many of which were bred for herding other animals.
For smaller dogs such as chihuahuas, training is still important to minimize nervous and destructive behaviors.
Merle Dog Activity
Again, how energetic your dog will be will probably be more dependent on breed than color.
Reducing Health Risks in Merle Dogs
Veterinarians recommend genetic testing for merle dogs.
Because the genetics of the merle coloring can be complicated. The variations of merle coloring can result in a variety of appearances, so testing may be the only way to understand the merle dog’s true genetic makeup.
Also, please don’t breed your merles, especially with other merles.
Certain dogs that don’t look like merles may actually still carry the M gene.
For example, cryptic merles or sable-colored dogs may be indistinguishable from non-merle dogs.
And, if not identified through genetic testing, someone unaware of the genetic background of their dogs might inadvertently mate two merles together, resulting in a litter that includes double merle dogs.
The genetics can be complicated, and breeding merles is for experts only!
Even experienced breeders are likely to experience setbacks and heartbreak.
Merle Dog Puppies
Merle coloring can become darker with age.
Just be aware that those white areas on your merle puppy may start to look grayer as your dog ages.
But other than that, a merle dog puppy will have all the attributes of an adult of the breed.
Color isn’t necessarily going to determine your dog’s longevity, temperament or the joy you take in being with her.
However, the merle gene itself does have health issues associated with it.
If you want a merle dog, do your homework. Get your puppy from an experienced breeder, and know its genetics.
How you care for your new merle puppy will definitely affect his quality of life, so make sure you are ready!
We’d love to hear about your merle dog if you decide to get one so drop us a comment below!
References and Resources
- American Dog Breeders Association, 2016, Health and the Merle Pattern.
- American Kennel Club, Australian Shepherd.
- Chappell, J. Merle (M series). Dog Coat Colour Genetics.
- UC Davis Veterinary Medicine Veterinary Genetics Laboratory, “Merle”.
- Australian Shepherd Health & Genetics Institute (2017). “Cryptic Merles”.
- Bowling, S. A.,2010, Sheltie Bloodlines, “Elementary merle genetics for newcomers”.
- Clark, L. A. et al,2006, Retrotransposon insertion in SILV is responsible for merle patterning of the domestic dog, Proceedings of the National Academy of Sciences of the United States of America.
- Gelatt, K. N. et al,1981, Inheritance of microphthalmia with coloboma in the Australian Shepherd dog, American Journal of Veterinary Research.
- Sponeneberg, P. and Lamoreux, M. L., Inheritance of tweed, a modification of merle, in Australian shepherd dogs. Journal of Heredity.
- Strain, G. M. et al, 2009, Prevalence of deafness in dogs heterozygous or homozygous for the merle allele, Journal of Veterinary Internal Medicine.