Merle color in dogs and its problems

Particularly appreciated for its beauty, the merle coat of dogs can pose significant he alth problems for the dogs concerned.

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What is merle color in dogs?

We speak of merle color when a dog has a coat whose background color is diluted in places and which gives the impression of being spotted in an irregular and variegated way.

There are two kinds of merle dresses:

  • merle red in which the coat is mostly brown or liver, variegated with yellow to red hairs,
  • blue merle which qualifies a predominantly blue coat (in fact a mixture of grey/black and white hairs) more or less dark, in which we find more or less extensive black spots.

Red or blue, dogs with merle coats have, for the vast majority of them, odd or blue eyes.

" When the blackbird color is hidden: the case of ghost blackbirds"

In some dogs, the areas of dark coat are so large that they can cover almost the entire body of the animal and hide the fact that it does indeed have a merle coat. We then speak of ghost blackbirds, hidden blackbirds or even cryptic blackbirds. Some of them don't even wear the merle color at all.

What dog breeds are concerned?

Dog breeds that can sport a merle coat include Australian Shepherds, Australian Cattle Dogs, Beaucerons, Border Collies, Shetland Sheepdogs, Shorthaired and Longhaired Collies, Great Danes, Pyrenean Shepherds, Welsh Corgi (Cardigan variety), Fox-Hounds, Dachshunds (dapple or spotted) and Chihuahuas.

What is the merle dress due to?

The merle color of dogs results from a variation on chromosome 10 called the M allele (for merle). The M allele influences the color of the canine coat by modifying the expression of a gene which is responsible for the production and storage of eumelanin (black pigment of the skin and hair).

It results in the dilution of the color of the dog's coat in patches.

A dog's "merle" trait is dominantly inherited, which means only one copy of the M allele is needed for a dog to sport a merle coat. If a dog is born merle, it must therefore have a merle parent who transmitted to it an allele M.

What's wrong with merle color?

When two dogs carrying at least one M allele (and therefore merles, whether red or blue merle) are mated, the risk is to produce a "double merle" puppy. i.e. carrying two copies of the M allele.Double merle dogs are also called MM homozygotes.

This genetic status is associated with a Merle color with invasive white and above all with significant risks of skin disorders as well as serious eye and hearing problems. Double merle dogs even have up to a 25% chance of being deaf.

Cryptic Merle Parents: Beware!

Cryptic merle dogs do not necessarily express a merle coat, but they do carry the cryptic Merle allele (Mc) in their DNA. The cryptic Merle copy (Mc) can be transmitted as a Merle copy (M) to offspring.

To avoid risky marriages, it is therefore recommended to have DNA tests performed on breeding animals in order to limit the risk of giving birth to double merle (MM) dogs, which can suffer from serious he alth problems.

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