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Merle is arguably the most fascinating and misunderstood coat pattern in the pet world. The conspicuous markings are only found in certain dog breeds; no other animal has this quality. Technically, the merle coat pattern can be bred in just about any line, but in practice, merle breeding is highly restricted to only certain breeds. This article covers some fascinating details about genetics, life expectancy, and the health issues associated with the merle coat.
What is a Merle Coat?
Merle can be defined as a mottled coat pattern that combines lighter and darker patches of the same color. The random patterns are usually unique to the dog, so no two layers can be exactly the same. The merle coat usually comes in red merle (which is more like liver) or blue merle (which is black or gray); this is surrounded by solid white areas. Dogs with the merle gene but little to no true merle patterns are called phantom merle or cryptic merle. The spots are so small that it hardly resembles a merle, but it can still pass the merle trait on to their offspring.
Over the years, two other types of merle variations have gained recognition beyond just the “standard” and cryptic merle types: these are called the diluted merle and the harlequin. The dilute merle has light red or black coat colors without any spots, while the harlequin has a white background with a few large spots of dark pigmentation. It may be hard to tell that these are merles as they don’t show the usual spotted pattern, but they do carry the modified merle gene which can be passed on to their offspring.
In addition to coat colors, the merle gene also changes the color of other parts of the body. The eyes are much more likely to be colored blue, while the nose and soles may have a more mottled pink appearance.
What is the correct pronunciation of Merle?
Merle’s pronunciation is as simple as it seems: it rhymes with “girl” or “hurl.” The modern word and its pronunciation probably come from the Latin name for the blackbird. It may have ended up in English through the French language in the Middle Ages.
How is the Merle Coat made?
The merle coat pattern stems from a change in the gene that produces black and brown pigments in the hair. Merle puppies will always inherit this modified strand of DNA while non-merle puppies will inherit DNA without the merle trait. This section gets a little technical about genetics. Essentially, all animals inherit two copies or variants of the same gene from both parents. These variants can be dominant or recessive, with the former usually expressing itself above the latter. If the progeny inherit two dominant copies or one dominant copy and another recessive, the dominant trait is expressed. If the offspring inherit two recessive copies, only the recessive trait is expressed.
The merle property works a little differently than this. It is what is known as incomplete dominance. This means that the recessive copy still affects the trait even in the presence of another dominant copy. If the offspring inherit two recessive copies of the merle gene, they will have little to no merle. But if it inherits a dominant specimen and a recessive specimen, then it will have a normal merle coat. If it inherits two dominant specimens, it will have a double merle coat. Despite the name, this double merle jacket hardly resembles a merle; it resembles the harlequin in that it has a lot of solid white fur and relatively few spots. The double merle is generally avoided by responsible breeders for health reasons (covered in the section below).
You may be wondering what the genetic difference is between a cryptic merle, a dilute merle, a common merle and a harlequin? The short answer to the question is that there are additional genetic factors that determine the amount of pigmentation, but that is beyond the scope of the article. Suffice it to say, it has something to do with the length of the DNA segment that produces the pigmentation. Shorter or longer segments have different effects on the patterns.
Based on all this information, it is quite easy to predict what the puppies will look like just by knowing the genetics of the parents. By crossing two regular merle dogs together (ie dogs with one dominant and one recessive merle trait), in an average litter you will have about half of the regular merle puppies like the parents, a quarter of non-merle puppies with two recessive copies, and a quarter of double merle puppies (ie two dominant copies).
Because of the health issues associated with the double merle coat, some breed clubs will even ban a merle-merle cross to prevent double merle puppies from appearing in the litter. They will instead recommend crossing a merle with a non-merle dog, which drastically reduces the chances of health problems.
If you are unsure about your dog’s genetic makeup, consider having a genetic test. Normal merles are fairly easy to identify, but cryptic merles and harlequins are particularly easy to confuse with other types of dogs. This may not matter much unless you plan to breed your dogs, in which case they could accidentally pass on merle traits without you realizing it.
Is the Merle coat rare?
It all depends on the breed in question. For some breeds, red or blue merle is one of the most common coat patterns. For other breeds, it’s kind of a new coat pattern, but not one of the most common coats. However, for most breeds, merle is completely banned by legitimate breeders. This makes it difficult to estimate how likely you are to find one. While most breeders try to avoid merles altogether, some specialize in breeding merles, so you may need to do some research first.
To help you through this difficult process, the best way to track down a new puppy is to contact a trusted breeder through the American Kennel Club or other breed-specific clubs. Breeders should be very knowledgeable and candid about the pros and cons of buying a merle. If you’re more interested in adopting instead, the odds of finding a merle dog depend a lot on the breed. Merle Aussies can often be found in kennels or rescues, while some breeds are much rarer.
What Dog Breeds Have a Merle Coat?
The merle coat is unique to certain types of sheepdogs and other closely related breeds. This is because the merle coat arose from a unique genetic change in a common ancestor of many modern herding breeds. The Australian Shepherd is probably the only breed that immediately comes to mind when someone mentions merle. Both red merle and blue merle are among the few accepted Aussie coat patterns. Other common merle breeds include: border collies, shetland sheepdogs, Great Danes, Dachshunds, Cardigan Welsh Corgis, and Catahoula Leopard Dogs.
While it is possible to breed a red and blue merle coat into other types of dogs (such as, say, a pit bull), which may disqualify them from purebred status in the eyes of many dog organizations. This can lead to serious difficulties in finding a reliable breeder because if the merle trait is not part of the breed standard, reputable breeders will usually not bother with it and open the door to all sorts of dodgy sources. In these cases, it’s even more important that you do your homework and ask the right questions (especially regarding the dog’s health and any tests they may have taken). Breeding pit bulls in particular can sometimes fall prey to these low standards. Be extra careful when buying Pitbulls.
Do Merle Coat Dogs Have Health Problems?
Merle dogs are thought to have a low risk of developing health problems, and their life expectancy is about the same as any other type of dog, but there is one exception: double merle dogs are much more likely to have vision and hearing problems. Several studies have been done to gain insight into the risks of a merle coat. One study found that a standard merle dog had a 2.7% chance of deafness in one ear and a 0.9% chance of deafness in both ears. The double merle dog (meaning that a dog inherits two dominant copies of the merle gene) had an astonishing 10% chance of deafness in one ear and 15% of deafness in two ears. Double merle dogs are also at risk of developing microphthalmia, in which the two eyes are unusually small and sometimes even nonfunctional. These risks also vary by breed. The rate of hearing impairment was particularly high in the double merle Australian Shepherds, but much lower in the double merle Catahoulas.
There is some debate about how serious the double merle trait is. It is generally true that most double merle dogs will lead a mostly healthy life with a normal life expectancy. It’s not a life-threatening problem at all. Still, there’s no reason to put a dog at risk for vision and hearing problems by breeding a double merle dog (especially since he doesn’t even produce the full merle coat colors).
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