The "Merle" Gene
Genotype is not the same then Phenotype!
The fur colour "merle"
The fur colour merle ís distinguished by a characterístic look regarding the colour pattern. In this case a dog shows larger and smaller areas with diluted pigment and others with full pigment. The gene responsible for the merle colour also causes a colour fading of the original fur colour. But comparing with other colour fading genes, this does not effect the whole fur, just several areas and spots which can be found in different patterns all over the dogs body. Merle also effects the eye colour. Merle-coloured dogs can have solid brown, blue oder mixed coulored eyes. They can even have more then one colour in one eye.
Cause
Merle is carried by a genetical change in the Silver-Gene (SILV, Pmel17). This is a mobile genetical element (Retrotransposon), that lays within the SILV-Gene and deranges its functionality. This for the merle colour responsible defect SILV-Gene is named with M, while the normal SILV-Gene is named with m. The typical merle fur colour originates in dogs which carry the mutant version of the SILV-Gene heterozygous (Mm). The defect SILV-Gene (M) shows an imperfectly dominant heredity.
Health issues
Dogs which carry the heterozygous mutant version of the SILV-Gene (MM, double merle), are mostly coloured white, or have great white areas on their body. These kind of dogs can have very severe damage and malformation of the internal ear which can lead to deafness or amblyacousia. In addition there can be malformations of the eyesight as well as anomalies of the sexual organs, the skeleton and even the heart. To prevent this defects from happening, you should avoid to breed two merle animals.
Cryptical merle
Even if its rare, but there are dogs which dont show the merle colour, but still carry the merle gene and when breed can have merle coloured offspring. Such dogs are called cryptical merle. Its assumed that cryptical merle dogs carry a specific merle gene which has a shortened mobile element in the SILV-Gene. A stabile genetical reversion, which means a spontanious loss of the disposition merle (M) ín the offspring of merle gene carrying dogs is documented in the medical literature by a percentage of 3-4%.
The following genotypes are possible
mm: The dog itself has the genetic preposition : Non-merle.
Mm: The dog itself has the genetic preposition: Merle.
MM: The dog itself has the genetic preposition: Double-merle
M(c)m: The dog itself has the genetic preposition: Non-merle (heterozygot „cryptical“ merle)
M(c)M(c): The dog itself has the genetic preposition: Non-merle (homozygot „cryptical“ merle)
M(c)M: The dog itself has the genetic preposition: Merle (heterozygot „cryptical“ merle)
Breeding with dogs that carry the merle gene
For breeding in general it might be important to know that dogs which carry the merle-gene (Mm; one normal and one mutant gene) will give the merle gene with a likelyness of 50% to their offspring. So there is a huge danger that when you breed two merle gene dogs together, an amount of the offspring might be double merles and those might have some of the health issues named above. But merle dogs dont have to be taken out of a breeding program. A breeder just has to pay attention that he breeds a mm dog (which carries two normal genetical copies) to a Mm or MM dog. If taken this into consideration the offspring can only carry non- merle (mm) and merle (Mm) genes. No double merles!
It would be a responsible decision by every person who is a breeder, to get their dogs tested so that they know which dog carries which gene, and to prevent sick and damaged puppies to be born!
Possible Genotyp-Combinations
|
Parent 1 |
Parent 2 |
Offspring |
|
mm = non merle |
mm = non merle |
100% of these dogs are mm = non merle→ carry the full pigment coating of the fur |
|
mm = non merle |
Mm = merle |
50% of these dogs are Mm = merle 50% of these dogs are mm = non merle → carry the full pigment coating of the fur |
|
mm = non merle |
MM = double merle |
100% of these dogs are Mm = merle |
|
Mm = merle |
mm = non merle |
50% of these dogs are Mm = merle 50% of these dogs are mm = non merle → carry the full pigment coating of the fur |
|
Mm = merle |
Mm = merle |
25% of these dogs are mm = no merle → carry the full pigment coating of the fur 50% of these dogs are Mm = merle 25% of these dogs are MM = double merle → Attention! Severe health damage can be caused! |
|
Mm = merle |
MM = double merle |
50% of these dogs are Mm = merle 50% of these dogs are MM = double merle → Attention! Severe health damage can be caused! |
|
MM = double merle |
mm = no merle |
100% of these dogs are Mm = merle |
|
MM = double merle |
Mm = merle |
50% of these dogs are Mm = merle 50% of these dogs are MM = double merle → Attention! Severe health damage can be caused! |
|
MM = double merle |
MM = double merle |
100% of these dogs are MM = double merle → Attention! Severe health damage can be caused! |
It`s a fact that:THE OPTICAL APPEARANCE DOES NOT TELL ANYTHING ABOUT THE GENETICAL SETUP OF A DOG! Just with an established genetical test you can prove what kind of gene each dog carries!
Such a genetical test comes along with costs of roughly 60 Euros. Which is not a lot if it will lead to healthy pups and if you can contribute to the wellfare of a breed of dogs in general!
In germany the following laboratories provide these tests:
Labokolin & Biofocus
"Patchwork merle"
"Solid brown"
"Merle colour"
