The dog world is full of astounding color variations and patterns, and merle is one of the most prominent unusual coat types. Dapple merle is the most well-known type of merle coat, with dappled gray spots against a lighter gray coat. In fact, merle is the contrast of a darker pigment against the same pigment in a lighter shade, not a specific color combo.

You can also see red merle coats that exhibit brown splotches against a lighter tan. The exact shade of the spots and the background color shift a bit, as do the size, spacing, and shape of the spots. One white dog may have countless Dalmatian-like spots, and another tan dog barely has any dark brown spots at all, but both dogs carry the merle gene!

Sometimes, merle dogs even have unusually dark eyes or heterochromatic odd-colored eyes. You may have heard that dogs with merle coats are more prone to certain health problems, and that’s true, too! Unfortunately, the merle gene is linked to a number of severe health conditions that affect the dog’s quality of life and makes breeding merle dogs an ethical quandary.

These health problems are mainly related to the eyes, ears, and skin. For an overview, check out a list of the most common health issues associated with the merle gene below.

Common Health Problems in Merle Dogs

Those are significant health problems, but how exactly does the merle gene cause them? Are you supposed to breed merle dogs with other merles or not? If you’ll humor us, we’ll wade into all that info and more about the merle gene below.

What Breeds Can Have Merle Coats?

As a quirk of genetics, some breeds are more likely to carry and pass on the merle gene than others. As with other genes, the merle gene can be passed to mixed dogs, making it essential to consider whether their purebred parents came from breeds that carry the merle gene. It’s also good for new dog owners to have a better idea of which dogs can suffer from partial deafness or eye problems due to a merle coat. Check out the breeds below for quick reference.

Merle Dog Breeds:

The Merle Coat & Genetics: How DNA Becomes Color

The merle gene’s scientific name is PMEL17. This gene normally helps produce eumelanin, which is responsible for producing black and brown coloration in the skin. A mutation called SINE insertion tips over this careful genetic sequence, causing a cascade of effects, including the unique merle coloration and the other health problems seen in merle dogs.

At its most basic, the merle gene suppresses or disrupts the production of melanin or color-carrying pigment in certain parts of the skin, leading to the signature merle gray-on-black spots. How a merle coat presents depends on whether a dog is a single merle or double merle. The difference? Single-merle dogs have one dominant merle gene from one parent and a recessive non-merle gene from the other, while double-merle pups have a dominant merle gene from both parents (MM).

Single-merle dogs have a wider range of color because the merle gene doesn’t uniformly suppress the skin pigment. For example, a tan and brown single merle dog can display up to four or more distinct shades, creating vivid contrast. These dogs are less at risk of the most severe side effects caused by the merle gene but are a little more likely to develop deafness. Single-merle dogs are generally more desirable because they have a pleasing coat pattern with minimal detrimental side effects.

The merle gene’s effects on double-merle dogs are much more obvious. The base skin color becomes white, and the gray spots are less obvious, with some dogs appearing all-white with very few small spots across the body. Double-merle dogs often have blue or heterochromatic eyes, and sadly, they’re small or deformed, a condition called microphthalmia. The risk of deafness is high, too. According to the AKC, 50% to 80% of double-merle Australian Shepherds studied were deaf in both ears.

Should You Breed Two Merle Dogs Together?

No, it’s considered ethically irresponsible to breed two merle dogs because of the higher risk of health problems. Even so, many shady dog breeders purposely breed merle dogs together to produce merle puppies that command high prices.

With a 1 in 4 chance of merle dogs being entirely deaf, there’s a tragically high risk of undesirable puppies being abandoned and put to sleep. While genetic screening can help minimize and identify the potential health risks in double-merle dogs, it’s ultimately not a very ethical practice.

Is the Merle Gene Related to Albinism? Merle vs. Albino Coats Explained

Double-merle coats are sometimes confused for albino coats because they have a distinct white base and a noticeable lack of pigmentation. This is especially common if their spots are very sparse and muted. It’s easy to see the confusion if you know little about merle or albino coats, but they’re completely separate phenomena!

Merle coats result from a mutated gene that produces less melanin in some parts of a dog’s skin and fur, while albino coats are caused by a genetic defect that causes the skin and fur to produce no melanin at all.

The difference is subtle but obvious once you see it. Albino dogs have snowy all-white coats with no spots and have blue or reddish-pink “albino eyes.” Like merle dogs, albinos have sensitive skin that burns easily with prolonged sunlight exposure.

Conclusion

The merle gene is responsible for some of the most stunning coat colors in the dog world but also some nasty side effects like deafness and blindness. While impossible to eliminate, these risks can be somewhat managed by encouraging people to breed single-merle dogs that generally lead healthier, happier lives than many double-merle dogs that develop health complications.

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Featured Image Credit: Christian Kohlhausen, Shutterstock