Understanding Merle (Dog Coat) Genetics

Merle dogs have a unique coat pattern, but have you ever wondered what makes it happen? The genetics behind the merle coat are complex, but it's rooted in the interaction of two types of melanin: eumelanin and phaeomelanin.

The merle gene is a type of allele that codes for the production of phaeomelanin, which is responsible for the red and yellow colors in a dog's coat. This gene is recessive, meaning a dog needs to inherit two copies of the gene (one from each parent) to express the merle coat.

The interaction between the merle gene and the eumelanin gene determines the final coat color. Dogs with the merle gene can also have a solid coat color, as long as they don't inherit the other necessary genes.

The merle coat color is caused by a dominant genetic factor, where only one mutated copy of the merle gene is required to produce an effect on coat color. This is known as a dominant genetic factor.

The merle gene is a semi-dominant gene, meaning it only takes one copy of the M allele to produce a merle. This is in contrast to a dominant gene, which would require two copies to produce the trait. Every merle dog has one copy of the merle allele (M) and one copy of the non-merle allele (m).

The merle allele was first discovered at Texas A&M University's College of Veterinary Medicine in 2006. The merle coat color is governed by a type of mutation called a SINE insertion in the SILV (also called PMEL17) gene.

The genetics of merle coat color can be complex, but it's essential to understand the basics to make informed decisions about breeding. By knowing the genotype (M/N or M/M) and phenotype (merle or non-merle) of a dog, breeders can make informed decisions about breeding to avoid health problems associated with double merle dogs.

Here's a quick rundown of the possible genotypes and phenotypes:

The merle allele is an incompletely dominant allele, meaning it doesn't completely mask the non-merle allele. If two heterozygote merle dogs are mated, on average, one-quarter of the puppies will be "double merles", which is the common term for dogs homozygous for the longest versions of the merle alleles.

Double merle puppies can have eye defects or be deaf, which is why knowledgeable and responsible breeders who want to produce merle puppies mate a merle with a non-merle dog.

The merle allele was first discovered at Texas A&M University’s College of Veterinary Medicine in 2006, where scientists found a mobile genetic unit called a retrotransposon responsible for the various merle mutations in dogs.

A phantom merle or cryptic merle is one with such small patches of merling, 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.

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The merle allele is a semi-dominant gene, meaning it only takes one copy of the M allele to produce a merle. Every merle dog has one copy of the merle allele (M) and one copy of the non-merle allele (m), meaning every merle dog has an Mm genotype.

Here's a summary of the merle gene mutation:

The merle mutation affects melanocytes, the cells that produce melanin pigment, and melanocytes are found not only in the skin but in the eye and inner ear, as well as the bones and heart.

The Genetics of Merle Coat is a complex topic, but let's break it down. Several loci can be grouped as affecting the shade of color, which is a crucial aspect of the merle coat.

The Brown (B) locus plays a significant role in determining the coat color. This is because the Brown locus affects the production of the pigment eumelanin, which is responsible for brown and black colors in the coat.

The Dilution (D) locus also impacts the coat color, making it lighter than usual. This is because the Dilution locus affects the amount of eumelanin produced, resulting in a lighter coat.

The Intensity (I) locus is another important factor in determining the coat color. This locus affects the intensity of the eumelanin, resulting in a more vibrant or dull coat color.

The merle coat pattern is a result of a dominant genetic factor that affects coat color. The merle gene is responsible for the characteristic patches of color on a dog's coat.

A merle dog has one mutated copy of the merle gene, which is enough to produce the merle effect. This means that a merle dog can be bred to a non-merle dog, resulting in 50% merle pups and 50% non-merle pups.

The merle gene is linked to the PMEL gene, which is responsible for the synthesis of melanin. The mutation in the PMEL gene causes changes in the colors and pattern of the coat, as well as the absence of pigmentation in the pigmented cells of the eyes.

The merle gene is semi-dominant, meaning it only takes one copy of the merle allele to produce a merle. Every merle dog has an Mm genotype, and every non-merle dog has an mm genotype.

A DNA test is required to detect the presence of the merle gene, especially in dogs that appear to be non-merle but may be cryptic merle. Cryptic merle dogs (Mc/N) can be mated with typical merle dogs (M/N), resulting in a high probability of congenital anomalies in the offspring.

Here's a breakdown of the possible genotypes and phenotypes of merle dogs:

The merle gene is associated with several health concerns, including hearing loss and microphthalmia. Double-merle dogs have a high probability of congenital anomalies, including blindness and deafness. It's essential to avoid breeding merle to merle to prevent these health issues.

The merle gene is a result of an insertion of a SINE sequence in the PMEL gene, which is found on canine chromosome 10. This mutation causes the characteristic patches of color on a merle dog's coat.

The merle gene is linked to the Harlequin (H) and Spotting (S) loci, which contribute to patching, spotting, and white markings.

Genetic testing can determine if a dog has the merle allele and its size, which affects the coat color and pattern.

A merle dog (M/N) must not be mated with another merle dog, as this can result in double merle puppies (M/M) with hearing and vision problems.

The M Locus DNA Test can ensure that a "normal" parent does not carry the mutated gene (cryptic merle) despite its normal appearance.

Genetic testing of the PMEL gene will determine whether a dog has no copies or one or more copies of the merle insertion variant.

A normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.

The merle allele is inherited in a dominant fashion, meaning only one copy of the M allele is necessary for a dog to display some variation of the merle coat color/pattern.

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The M variant of PMEL typically affects only eumelanin pigmented areas and not phaeomelanin (yellow/red) pigmented areas.

The size of the M allele(s) present in a dog have been associated with different merle coat colors/patterns.

Here are the possible genotypes and phenotypes of merle dogs:

This table shows the possible genotypes and phenotypes of merle dogs, which can help breeders understand the genetic basis of the merle coat color.

Genetic testing can also help identify phantom merle or cryptic merle dogs, which have small patches of merling or none at all, but can still carry the M allele and produce merles.

It's essential to DNA test before breeding any dog from a breed or family known to produce merle, as a DNA test can tell you if your dog has zero, one, or two M alleles.

The merle coat color is a result of a dominant genetic factor, where only one mutated copy of the merle gene is required to produce an effect on coat color.

Merle is an incompletely dominant allele, meaning that two heterozygote merle dogs mated together will produce a litter with a high percentage of double merle puppies, who can have eye defects or be deaf.

The merle allele is governed by a type of mutation called a SINE insertion in the SILV (also called PMEL17) gene, which was first discovered at Texas A&M University's College of Veterinary Medicine in 2006.

A merle dog has one copy of the merle allele (M) and one copy of the non-merle allele (m), resulting in an Mm genotype.

Dogs with two merle alleles (MM), also known as double merles, don't look like merles and usually have much more white on them.

Here's a breakdown of the possible genotypes and phenotypes resulting from merle matings:

Genetic testing can identify the merle allele and prevent the birth of double merle dogs, who can have eye defects or be deaf.

Genetic testing has revolutionized the way we understand and predict the merle coat color in dogs. By determining the presence and size of the M allele, breeders can make informed decisions about breeding.

The M Locus (Merle) coat color test is a reliable method for identifying dogs that carry the M allele. This test can also determine the approximate size of the M allele(s).

The merle allele is an incompletely dominant allele, meaning that the expression of the merle coat color is influenced by the presence of other genes. This is why breeding two heterozygote merle dogs can result in a high percentage of double merle puppies with vision or hearing defects.

Genetic testing can identify the presence of the M allele, but it cannot predict the exact expression of the merle coat color. However, by understanding the genetic basis of the merle allele, breeders can make informed decisions about breeding.

Here's a rough estimate of the frequency of different merle phenotypes and genotypes:

Genetic testing and phenotype prediction can be complex, but it's essential for responsible breeding practices. By understanding the genetic basis of the merle allele, breeders can reduce the risk of producing double merle puppies with vision or hearing defects.

Merle can affect all coat colors, including brown, which is often mislabeled as "red" due to a genetic difference from true red.

The merle pattern modifies eye color and coloring on the nose and paw pads, resulting in eyes or parts of eyes turning blue, and pigmentation on paw pads and nose may be mottled by pink.

In addition to its effects on coat color, merle also affects the eye color, with dark-eyed, blue-eyed, and odd-colored eyes possible.

Merle is a distinguishing marking of several breeds, particularly the Australian Shepherd and Catahoula Leopard Dog, and appears in others, including the Miniature American Shepherd and the Shetland Sheepdog.

In some breeds, the merle pattern is known by different names, such as "dapple" in Dachshunds and "harlequin" in Beaucerons.

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Merle can affect all coat colors, including red, which is actually genetically different from brown.

The merle form of black is often called "blue" because of the lighter patches of black that give it a slightly blue appearance.

Dogs with recessive red coats can still be affected by merle, but the patches may be hard to see or invisible altogether.

Merle also modifies eye color, resulting in eyes that can be blue, dark-eyed, or even odd-colored.

Pigmentation on paw pads and nose may be mottled by pink due to the merle allele's effect on dark pigment.

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The merle pattern is a distinctive marking found in several dog breeds. The Australian Shepherd and Catahoula Leopard Dog are two breeds where merle is particularly common.

Merle also appears in the Miniature American Shepherd, the Koolie, the Shetland Sheepdog, and various collie breeds. These breeds showcase the versatility of the merle pattern.

The Cardigan Welsh Corgi and the Pyrenean Shepherd are two more breeds where merle is a notable feature. The Bergamasco Shepherd is another breed that features this unique pattern.

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In some breeds, the merle pattern is known by different names, such as "dapple" in Dachshunds or "harlequin" in Beaucerons. The Great Dane is another breed where the merle pattern is known as "harlequin".

The merle pattern is not always recognized by breed standards, which can affect a dog's eligibility for showing. In some cases, dogs with the merle pattern may be allowed to register with a kennel club, but only if they meet specific requirements.