Is the Merle Gene Bad? We Investigate

What is the Merle Gene?

Merle, as you might be aware is a particularly striking coat color/pattern seen in many breeds of dogs including Poodles and consequently Doodles. Merle dogs have a very beautiful distinctive mottled patterned coat, usually with a blue-grey base but they can also be red or black.

They often have blue or odd eyes like those often seen in Huskies or Collies and pink freckled noses. The merle color is very attractive to puppy buyers and some breeders charge a premium for merle puppies.

The merle gene itself is not a color as such but is a modifier gene that changes the base color of the coat and controls the distribution of pigment. This gene mutation is an ‘incomplete dominant’ or heterozygous which means the dog only needs to inherit one copy to be merle.

A dog that inherits this gene will show as merle and carry merle, however, he may not pass on the gene to all of his offspring as he also carries a copy of the non-merle gene.

If a dog inherits two copies of the merle gene, they will be homozygous for merle which means they will pass on the gene to 100% of their offspring. This is also known as double merle.

Is Merle a Defect?

The merle gene is not a defect and in fact, in some breeds, merle is included in the breed standard and is a recognized color. You will even see merle dogs of some breeds in the show ring if merle is naturally occurring within the breed and has not been introduced via cross-breeding.

Breeds such as Australian Shepherd, Beauceron, Bergamasco, Border Collie, Cardigan Welsh Corgi, Dachshund (the color is known as dapple), Great Dane, Long Haired Pyrenean Sheepdog, Rough Collie, Shetland Sheepdog, and Smooth Collie are accepted for registration.

In the UK other breeds will be rejected from being registered if they are merle. However, the AKC does not withhold registration from any purebred dog based on color if that dog would otherwise be eligible for registration. Therefore, merle dogs of any breed can be registered.

However, if merle is not on the list of recognized colors for that breed the dog will not be able to be shown in the conformation ring.

So, you see merle is not a defect, but it is not without problems.

Does the AKC Recognise Merle Poodles?

Merle is not found on the AKC breed standard list of recognized colors. However, you can register merle Poodles with the AKC. To do this you must have the relevant AKC paperwork proving that both parents are registered.

The AKC recognizes many colors that the English Kennel Club does not, such as Parti Color and Phantom. They will allow breeders to register their pups as the recognized color closest to their actual color. For example, a merle Poodle may be registered as black and silver or brown and tan regardless of the markings he displays.

What is the Difference Between Brindle and Merle?

Two colors that are often confused are brindle and merle. Whilst both are rare and striking, they are different as brindle is a base color patterned with characteristic tiger stripes, usually black. Merle is random splodges of a darker color decorating the base.

Both are coat patterns rather than colors, but brindle has a wild-type allele which is the product of two recessive genes. In comparison, merle is a dominant gene (incomplete dominant).

Brindle is accepted and often seen in many breeds in the show ring. Interestingly it is also very common in mixed breed village dogs found roaming the streets in countries where stray dog populations are rife.

It is even possible for dogs to be both brindle and merle as merle is a gene modifier that affects pigment causing areas of the body to be completely devoid of any pigment (think of bleach poured on colored fabric).

What is a Hidden or Cryptic Merle?

You may have heard the term hidden or cryptic merle and wondered what this means. Quite simply the dog is merle, but the merle pattern is hidden or so reduced that it is not visible. It could even be that in a docked breed the only visible merle pattern was on the tail and once docked the merle pattern has gone.

Merle can also be masked by other colors such as true reds or creams where the color can be masking the pattern. The only way to identify these dogs as merle is by DNA testing. For this reason, it is vital that all dogs with merle in their ancestry are tested prior to breeding.

It can be especially difficult to detect merle in a heavily patterned coat using the naked eye. This is because if a dog is brindle, sable, or particolored with only a tiny amount of mottling it can easily be lost in the pattern.

Even more so in the case of long or curly-coated breeds like the Poodle. You may be wondering why this is important, especially if the visible merle is so tiny in the amount, it can’t be seen. Continue reading to discover why it is so important to be aware of merle.

What is a Double Merle and is it Bad?

A double merle is a dog that has inherited two copies of the merle gene, one from either parent. Double merle is homozygous meaning that this dog would pass on a copy of the merle gene to 100% of its offspring.

Why is this bad I hear you say? Surely as merle is beautiful and if you want to breed a merle you want to be guaranteed a particular dogs’ offspring will be merle, right? Wrong! Merle whilst beautiful can be lethal.

You may even have heard the term ‘lethal white’. Lethal white sounds like something from a shark movie and indeed it can be deadly. Double merle dogs often have predominantly white coats with very little other color showing and may have blue eyes and pink (non pigmented) noses, lips, and eye rims.

The appearance of the dog is not the problem however but rather the problem is with the pigment-producing cells or melanocytes. The melanocytes in the inner ear convert sound waves into electrical pulses that are sent to the brain and then interpreted into sound. A double merle dog can have very few or no melanocytes in the inner ear which means he can not hear. This can even lead to reduced blood supply and death of the nerve cells inside the ear.

Double merles are also more likely to suffer from eye defects including irregular or abnormal development of the iris and pupils causing partial or complete blindness. Some double merle dogs even have visibly deformed eyes.

The exact reason behind the visual impairment is not known but it is recognized that there is a link between double merle and blindness. A dog that has hearing and sight problems is undoubtedly going to have a compromised quality of life and it is difficult to place these dogs in homes that are able to care for them. Many breeders used to euthanize double merle pups shortly after birth, hence the term ‘lethal white’.

Thanks to modern science and genetic testing this is largely unheard of nowadays as ethical breeders of merles will test all dogs that have merle in their ancestry, even if it is not seen, to ensure that no pups are born carrying two copies of the merle gene.

Even more insidious than blindness and deafness are reports that double merle dogs have been reported to suffer from skeletal defects, kidney problems, neurological issues, allergies, and even early death. However, these are based on anecdotal reports from breeders and owners rather than scientific evidence. Even so, this must not be dismissed, and double merle dogs are not eligible for registration and should never be bred deliberately.

The basis on which any ethical breeder bases his breeding program should always be health before perceived beauty. While many people have adopted double merle dogs that have gone on to have great lives there is no doubt that we should be trying to avoid bringing pups with potential health problems into the world.

Fashion, unfortunately, dictates in the world of dog breeding and rare colors, or those considered especially beautiful such as blue eyes and largely white coats in breeds that are not usually white command high price tags. It is not unusual to see double merle pups being advertised for sale for double, triple, or more times the price of standard-colored pups.

This is a very sad and worrying trend and something that no ethical breeder would get involved in. This is one of the reasons that the registration of merle dogs is considered controversial. In some online forums discussing merle is banned and anyone that is seen to be breeding merle dogs or is ‘pro merle’ will risk heavy criticism or even a block from the group.

Specifically, in the world of Doodles which cannot be registered and have no governing body, merle is a problem that is on the increase particularly if breeders do not carry out color testing as well as health testing on their dogs.

Double Merle Life Expectancy

We accept that the quality of life for a dog that is blind, deaf, or both may be affected but does this have an impact on the dog’s life expectancy? The most obvious reason that the life expectancy could be shortened is accidents.

A deaf dog if he escapes from the home or secured yard, is unable to hear his owner calling him and is more likely to run off. He also may be unaware of danger such as approaching traffic and is, therefore, more likely to be hit by a car.

If the dog is also unable to see, then this danger is increased tenfold. While being visually or audibly impaired in itself does not affect his lifespan directly he is sadly more likely to be fatally injured in an accident.

It has also been reported that double merle dogs are more likely to be euthanized because of behavioral problems. Again, whilst behavioral problems are not a direct result of a dog’s color a dog that can’t see or hear needs special handling and could easily be startled by someone that does not approach him properly. A frightened dog may react by snapping or even attacking out of fear.


In summary, beauty is in the eye of the beholder. Whilst I personally believe merle dogs to be very beautiful it is a color that must be taken at more than face value. Incorporating merle into a breeding program must only be undertaken by experienced and ethical breeders who are willing to carry out testing on their dogs and would not consider taking their bitches to a merle stud without seeing evidence that he is a single merle rather than a double merle.

Remember cryptic merle exists and for this reason, testing for traits such as color must always be carried alongside genetic health testing. Approached carefully and ethically we should be able to enjoy these beautiful dogs of many colors without compromising the health of our beloved canines.