Merle GenXXX

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THE MERLE GEN

Not all genotypes are the same!

 

The coat color “Merle”

The coat color Merle is characterized by a characteristic coat covering, with spots of diluted color pigment together with areas full of pigmentation. The gene responsible for Merle staining causes the color to dilute the color that is normally present. But unlike other paint thinning genes, the effect is not distributed over the entire coat, but is only found in spots that can be distributed over the entire body. Merle also has an impact on eye color. Merle-colored animals can have solid brown, solid blue, or mixed colored eyes (one blue and one brown eye, or both colors in one eye).

 

root cause

Merle is caused by a genetic change in the silver gene (SILV, Pmel17). This is a mobile genetic element (retrotransposon) that is integrated into the SILV gene and thus disrupts its function. The defective SILV gene responsible for the Merle staining is abbreviated with M, while the normal SILV gene is abbreviated with m. The typical merle coat color arises in animals that carry the mutated SILV gene heterozygous (mixed blood) (Mm). The defective SILV gene (M) shows an imperfectly dominant inheritance.

 

Health consequences

Animals that genetically carry the mutated SILV gene (MM, double merle) are mainly colored white and can have severe malformations of the inner ear that lead to hearing loss or deafness. In addition, malformations of the eye can occur, as well as abnormalities of the reproductive tract, skeleton and heart. In order to prevent these defects, Merle x Merle crossings should be avoided. Merle is not expressed in animals that carry e / e at the e-locus (MC1R). Crosses of Merle animals with e / e animals (coat color clear red) that have not been tested on Merle should therefore also be avoided. The same goes for coat colors in which merle is difficult to identify such as fawn, cream, dapple and light sable.

 

Cryptic merle

Although rare, a dog may not have the merle color itself, but still carry the genetic make-up for merle and then also produce merle offspring. Such animals are called cryptic merle animals. It is believed that in cryptic Merle dogs, the mobile genetic element in the SILV gene is shortened. A stable genetic reversion, ie a spontaneous loss of the Merle (M) genetic make-up in the offspring of Merle carriers is documented in the literature with an (assumed) rate of 3-4%.

 

The following genotypes are possible

mm: The animal is pure breeding for the wild type allele. The system for the fur color merle is not available. The animal has its own coat color: non-merle.

 

Mm: The animal is mixed-blood carrier of the defective SILV gene responsible for the Merle staining and of the normal gene. The predisposition for the coat color merle is inherited by the offspring with a 50% probability. The animal itself has the color of its coat: merle.

 

MM: The animal carries the defective SILV gene responsible for the Merle staining. There is a 100% probability that the trait for the coat color merle is passed on to the offspring. The animal itself has the same color of fur: double merle

 

M (c) m: The animal is a mixed-blood carrier for the “cryptic” merle gene and the normal gene. The cryptic merle gene is inherited by the offspring with a 50% probability. The animal has its own coat color: Non-Merle (heterozygous “cryptic” Merle)

 

M (c) M (c): The animal is true breeding for the “cryptic” merle gene. The cryptic merle gene is inherited by the offspring with 100% probability. The animal has its own coat color: Non-Merle (homozygous “cryptic” Merle)

 

M (c) M: The animal is mixed for the “cryptic” merle gene and the merle defect gene responsible for the merle coloration. The merle defect gene (and the cryptic merle gene) is inherited by the offspring with a 50% probability. The animal has its own coat color: Merle (heterozygous “cryptic” Merle)

 

Breeding with merle carriers

It is crucial for breeding that Merle animals (Mm; carry a mutated gene and a normal gene) pass on the Merle genetic make-up to their offspring with a probability of 50%. When two Merle animals are mated, there is therefore the risk that some of the offspring are pure-bred, double-merle animals, which can have the health impairments mentioned above. Merle animals do not have to be excluded from breeding. If these are mated with a mm animal (carries two normal gene copies), the offspring can only consist of non-merle (mm) and merle animals (mm). For the breeder, the early knowledge of the genetic disposition of his animals is of particular importance. The genetic test provides clear information about the presence of the mutation mentioned. The breeder can plan possible matings with due regard to the information about the genetic predisposition.

 

For the reasons mentioned, a responsible breeder will not breed any animal with any other Catahoula without a prior genetic test in order to avoid the problems of pure-bred Merle animals!

 

Possible genotype combinations

Parent 1 Parent 2 progeny
mm = non merle mm = non merle 100% of the dogs are mm = non merle → carriers of full pigmentation of the fur
mm = non merle Mm = merle

50% of the dogs are Mm = merle  

50% of the dogs are mm = non merle → carriers of full pigmentation of the fur

mm = non merle MM = double merle 100% of the dogs are Mm = merle
Mm = merle mm = non merle

50% of the dogs are Mm = merle  

50% of the dogs are mm = non merle → carriers of full pigmentation of the fur

Mm = merle Mm = merle

25% of the dogs are mm = no merle → carriers of full pigmentation of the fur 

50% of the dogs are Mm = merle

25% of the dogs are MM = double merle → Attention! serious damage to health possible!

Mm = merle MM = double merle

50% of the dogs are Mm = merle 

50% of the dogs are MM = double merle → Attention! serious damage to health possible!

MM = double merle mm = no merle 100% of the dogs are Mm = merle
MM = double merle Mm = merle

50% of the dogs are Mm = merle 

50% of the dogs are MM = double merle → Attention! serious damage to health possible!

MM = double merle MM = double merle 100% of the dogs are MM = double merle → Attention! serious damage to health possible!

 

The fact is: THE OPTICAL APPEARANCE DOES NOT SAY ANYTHING ABOUT A DOG’S GENETIC CONDITIONS! Only a well-founded genetic test can prove which genes each individual animal carries!

 

A genetic test has a cost of around 60 Euros per animal. A small price to pay for the health of puppies and the opportunity to contribute to the welfare of an entire breed of dog!

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