Merle (coat colour in dogs)
Encyclopedia
Merle is a pattern in a dog
s coat
, though is commonly incorrectly referred to as a color.
.
In addition to altering base coat color, merle also modifies eye color and coloring on the nose and paw pads. The merle gene modifies the dark pigment in the eyes, occasionally changing dark eyes to blue, or part of the eye to be colored blue. Since merle causes random modifications, however, both dark-eyed, blue-eyed, and odd-colored eyes
are possible. Color on paw pads and nose may be mottled pink and black.
, and appears in others, including the Koolie
, German Coolies in Australia, the Shetland Sheepdog
, various Collie
s, the Welsh Corgi (Cardigan), the Pyrenean Shepherd
, the Bergamasco Sheepdog, the Old English Sheepdog
, and Catahoula Leopard Dog
. In Dachshunds the merle marking is known as "dapple". It is also present in the Pomeranian
and Chihuahua
, but is a disqualification according to the FCI
standards. In the American Pit Bull Terrier
, and Cocker Spaniel breeds it is not a recognized color. The merle gene also plays a part in producing harlequin Great Dane
s.
. If two such dogs are mated, on the average one quarter of the puppies will be "double merles", which is the common term for dogs homozygous for merle , and a high percentage of these double merle puppies could have eye defects and/or be deaf. Knowledgeable breeders who want to produce merle puppies mate a merle with a non-merle dog; roughly half the puppies will be merles without the risk of vision or hearing defects associated with double merle dogs.
In January 2006 scientists at Texas A&M University
announced the discovery of a mobile genetic unit called a retrotransposon
, responsible for the merle mutation in dogs.
A phantom merle or cryptic merle is one with such small patches of merle—or none at all—that it appears to be a non-merle. This is commonly seen in dogs who are recessive red, clear recessive reds in particular, though patches can still be seen in certain red dogs. In America, a dog with the phantom merle coloring is described as being "cryptic for merle."
of the cochlea
(inner ear) leads to blue eyes and deafness. An auditory-pigmentation disorder in humans, Waardenberg syndrome, reflects some of the problems associated with heterozygous and homozygous merle dogs and genetic research in dogs has been undertaken with the goal of better understanding the genetic basis of this human condition.
Deaf, blind, and deaf and blind dogs can have good lives when properly cared for. There are a variety of internet groups dedicated to supporting carers of such dogs. Deaf dogs can compete successfully in agility and there are many anecdotal reports of deaf/blind dogs earning their Canine Good Citizen
certification, working as therapy dogs, and competing in dog sports like tracking or Nosework.
Dog
The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
s coat
Coat (dog)
The coat of the domestic dog refers to the hair that covers its body. A dog's coat may be a double coat, made up of a soft undercoat and a coarser topcoat, or a single coat, which lacks an undercoat...
, though is commonly incorrectly referred to as a color.
Description
Merle can affect all coat colors but the colors most commonly seen that are affected are brown and black, when affected by merle they are usually called liver and blue, though some call liver red. Dogs who are recessive red can still be affected by merle, but the patches are either hardly seen or if the dog is a clear recessive red, it is not visible at all. Combination's such as brindle merle exist, but are not typically accepted in breed standardsBreed standard (dogs)
A breed standard in the dog fancy is a set of guidelines covering specific externally observable qualities such as appearance, movement, and temperament for that dog breed...
.
In addition to altering base coat color, merle also modifies eye color and coloring on the nose and paw pads. The merle gene modifies the dark pigment in the eyes, occasionally changing dark eyes to blue, or part of the eye to be colored blue. Since merle causes random modifications, however, both dark-eyed, blue-eyed, and odd-colored eyes
Heterochromia
In anatomy, heterochromia refers to a difference in coloration, usually of the iris but also of hair or skin. Heterochromia is a result of the relative excess or lack of melanin...
are possible. Color on paw pads and nose may be mottled pink and black.
Breeds
Merle is a distinguishing marking of several breeds, particularly the Australian ShepherdAustralian Shepherd
The Australian shepherd is a breed of herding dog that was developed on ranches in the Western United States. Despite its name, the breed, commonly known as an Aussie, did not originate in Australia They acquired their name because some of the Australian sheepdogs arrived in the United States with...
, and appears in others, including the Koolie
Koolie
The Koolie or Coolie, also known as the Australian Koolie or the German Koolie is an Australian dog breed. Specifically, it is a herding dog, a subcategory of a working dog...
, German Coolies in Australia, the Shetland Sheepdog
Shetland Sheepdog
The Shetland Sheepdog, often known as the Sheltie, is a breed of herding dog.They are small to medium dogs, and come in a variety of colors, such as sable/white, tri-color, and blue merle. They are vocal, excitable, energetic dogs who are always willing to please and work hard...
, various Collie
Collie
The collie is a distinctive type of herding dog, including many related landraces and formal breeds. It originates in Scotland and Northern England. It is a medium-sized, fairly lightly built dog with a pointed snout, and many types have a distinctive white pattern over the shoulders. Collies...
s, the Welsh Corgi (Cardigan), the Pyrenean Shepherd
Pyrenean Shepherd
The Pyrenean Shepherd is a medium-small breed of dog native to the Pyrenees mountains in southern France and northern Spain, bred since at least medieval times for herding livestock, especially sheep...
, the Bergamasco Sheepdog, the Old English Sheepdog
Old English Sheepdog
The Old English Sheepdog is a large breed of dog which was developed in England from early herding types of dog. The Old English Sheepdog has very long fur covering the face and eyes...
, and Catahoula Leopard Dog
Catahoula Leopard Dog
The Louisiana Catahoula Leopard Dog or Catahoula cur is an American dog breed. It is named after Catahoula Parish in the state of Louisiana in the United States. The Catahoula is believed to have occupied North America the next longest after the dogs descended from Native American-created breeds...
. In Dachshunds the merle marking is known as "dapple". It is also present in the Pomeranian
Pomeranian (dog)
The Pomeranian is a breed of dog of the Spitz type, named for the Pomerania region in Central Europe . Classed as a toy dog breed because of its small size, the Pomeranian is descended from the larger Spitz type dogs, specifically the German Spitz...
and Chihuahua
Chihuahua (dog)
The ' is the smallest breed of dog and is so named for the state of Chihuahua in Mexico. Chihuahuas come in a wide variety of sizes, head shapes, colors and coat lengths.-History:...
, but is a disqualification according to the FCI
Fédération Cynologique Internationale
Fédération Cynologique Internationale is an international federation of kennel clubs based in Thuin, Belgium. The English language translation, World Canine Organisation, is not often used.Its goals are described in Article 2 of their regulations:...
standards. In the American Pit Bull Terrier
American Pit Bull Terrier
The American Pit Bull Terrier is a medium-sized, solidly built, short haired dog whose early ancestors came from England and Ireland...
, and Cocker Spaniel breeds it is not a recognized color. The merle gene also plays a part in producing harlequin Great Dane
Great Dane
The Great Dane , also known as German Mastiff or Danish Hound , is a breed of domestic dog known for its giant size...
s.
Genetic basis
Merle is actually a heterozygote of an incompletely dominant geneGene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
. If two such dogs are mated, on the average one quarter of the puppies will be "double merles", which is the common term for dogs homozygous for merle , and a high percentage of these double merle puppies could have eye defects and/or be deaf. Knowledgeable breeders who want to produce merle puppies mate a merle with a non-merle dog; roughly half the puppies will be merles without the risk of vision or hearing defects associated with double merle dogs.
In January 2006 scientists at Texas A&M University
Texas A&M University
Texas A&M University is a coeducational public research university located in College Station, Texas . It is the flagship institution of the Texas A&M University System. The sixth-largest university in the United States, A&M's enrollment for Fall 2011 was over 50,000 for the first time in school...
announced the discovery of a mobile genetic unit called a retrotransposon
Retrotransposon
Retrotransposons are genetic elements that can amplify themselves in a genome and are ubiquitous components of the DNA of many eukaryotic organisms. They are a subclass of transposon. They are particularly abundant in plants, where they are often a principal component of nuclear DNA...
, responsible for the merle mutation in dogs.
A phantom merle or cryptic merle is one with such small patches of merle—or none at all—that it appears to be a non-merle. This is commonly seen in dogs who are recessive red, clear recessive reds in particular, though patches can still be seen in certain red dogs. In America, a dog with the phantom merle coloring is described as being "cryptic for merle."
Health issues
The merle gene is often associated with congenital deafness, with merle dogs being more likely than other dogs to be born deaf. Dogs with two copies of the merle gene (homozygous merle) have an even higher chance of being born deaf. The suppression of pigment cells (melanocytes) in the iris and in the stria vascularisStria vascularis
The upper portion of the spiral ligament contains numerous capillary loops and small blood vessels, and is termed the stria vascularis. It produces endolymph for the scala media, one of the three fluid-filled compartments of the cochlea...
of the cochlea
Cochlea
The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....
(inner ear) leads to blue eyes and deafness. An auditory-pigmentation disorder in humans, Waardenberg syndrome, reflects some of the problems associated with heterozygous and homozygous merle dogs and genetic research in dogs has been undertaken with the goal of better understanding the genetic basis of this human condition.
Ocular Defects
Dogs who are homozygous for the merle pattern gene often have visual and auditory deficits. These dogs are sometimes referred to as 'double merle' and sometimes incorrectly referred to as 'lethal white.' Ocular defects include micropthalmia, conditions causing increased ocular pressure, and colobomas, among others. Double merle dogs may be deaf or blind or both, and can carry ocular defects in blue or colored eyes. Currently no studies have been done to prove whether or not the merle gene affects the eyes, causing blindness.Auditory Defects
One study done by a German researcher showed that out of 38 dachshunds, they found hearing loss in 54.6% of double merles, and 36.8% of single merles. However, this percentage was based on one of the dogs and its hearing range, not the standard. The actual results were 9.1% of the double merles was deaf, that percentage being one, and 0% of the single merles were deaf. Another study done by Texas A&M University found that out of 22 double merles, 8 were completely deaf and two were deaf in one ear. Out of 48 single merles, only one was deaf in one ear, none were completely deaf. Another study done with 70 dogs, 15 of them were Catahoula Curs and 4 of them were deaf, whereas the other 86% of double merles in other breeds were deaf.Deaf, blind, and deaf and blind dogs can have good lives when properly cared for. There are a variety of internet groups dedicated to supporting carers of such dogs. Deaf dogs can compete successfully in agility and there are many anecdotal reports of deaf/blind dogs earning their Canine Good Citizen
Canine Good Citizen
The Canine Good Citizen program, established in 1989, is an American Kennel Club program to promote responsible dog ownership and to encourage the training of well-mannered dogs...
certification, working as therapy dogs, and competing in dog sports like tracking or Nosework.
External links
- Merle dog coat color genetics
- Deafness in Dogs and Cats
- White Aussies Project
- Genetics of merle dogs: Basic, simple-language explanation of Australian Shepherd merle colorings
- Homozygous "Lethal White" Merles