What do cross-eyed puppies look like

Merle factor in dogs

Everyone admires them - whether they are Chihuahua, Australian Shepherd, Dachshund or Great Dane lovers. However, many dog ​​lovers are not aware that the coat markings were only caused by a genetic defect. You can find out exactly what this magnificent coat is all about here.

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Radiant blue eyes and unusual patterns in the fur

They are fast, smart and funny - the Australian Shepherd is a well-known and currently one of the most popular dog breeds in Germany. They are loyal companions for sports, hiking tours and, of course, ideal as herding dogs. The Fédération Cynologique Internationale (FCI) has specified the following colors in the breed standards for these beautiful dogs: blue merle, red merle, black and red, with white and copper-colored markings being allowed.

Anyone who has ever met a merle will certainly share the enthusiasm for this unusual color. It is not for nothing that it is currently very fashionable and welcomed by breeders. Without question, the Merles are something special and beautiful to look at. Merle describes a dog whose fur has a clear grain in the areas that are usually brown or black. Most dogs with the genetic defect have one or two blue eyes. However, the beauty of these dogs also has some pitfalls. Because the inheritance of the genetic defect carries very great health risks with it. But let's start at the very beginning ...

What is the Merle Factor exactly?

With the expression Merle factor is called a Mutation on the dog's chromosome 10. It's on this chromosome SILV gene, also Silver Locus called. The genetic defect is inherited by incorporating a small piece of DNA that does not actually belong in this location in the genome into the silver locus. This so-called SINE (short interspersed nuclear element) - Insertion contains a more or less long piece of DNA that consists of only one DNA building block (base thymine). The longer this particular piece of DNA, the more pronounced the Merle coloration.

The defect in the SILV gene affects the pigment Eumelaninthat together with Pheomelanin is responsible for the color of the coat. Eumelanin takes care of the black and brown fur and eyes color. Will the Expression of eumelanin in the dog's body is disturbed, dark pigments cannot form in different regions of the animal and the fur becomes light. This is how the beloved piebald in Merle fur is created. The name is probably a derivation of the word "marbled" from English and means "marbled". Phaeomelanin is not affected by this genetic defect. This pigment causes a reddish-brown coat color, whereby areas, the color of which is determined by pheomelanin, are colored red-brown throughout.

How is the Merle factor inherited?

The Merle factor is inherited as an autosomal intermediate. Autosomal means that the defect is not on a sex chromosome, so the inheritance is not gender-dependent. Intermediate describes that the gene is incompletely dominant. In order to be able to explain this, one has to go back further.

The white dog in the picture with the genetic material (M I M) is a homozygous merle. The M denotes the chromosome that expresses the defect gene. The dog has two “diseased” chromosomes and is most likely to have serious eye problems. The brown dog in the picture is a homozygous dog with no coloring, it carries the healthy genetic material without genetic defects (m I m).

The two dogs are crossed with each other and there are four patterned offspring (see pictures) with the coloring. Since they each inherit one gene from the mother and one gene from the father, they are now mixed-breed (heterozygous). They carry a healthy m-gene and a diseased M-gene. Now it becomes clear why the Merle inheritance is referred to as intermediate. The healthy and the diseased genes mix, which means that there are both normally colored and mottled areas in the coat.

However, it becomes dangerous if you mate two animals with Merle spotting:

The two patterned parent animals are heterozygous merles with merle coloring. Now it's getting a bit complicated. The mixed hereditary carriers each transfer one of their gene expressions m or M to the offspring. This results in a probability distribution as to which genetic material each individual puppy can receive in the litter.

  • With a probability of 25% (chance 1: 4) a purely healthy young dog is the product of this pairing. It carries the genes (m I m) and is colored brown in the figure.
  • With a probability of 50% (chance 1: 2) the puppy can become a merle color if it inherits the heterozygous gene mixture (M I m), so these puppies carry a healthy and a diseased gene.
  • With a probability of 25% (chance 1: 4) both diseased M-genes are transmitted to the offspring, so that a pure merle with severe restrictions "arises" (white dog in the picture).

This probability is very high and therefore two Merle tigers should never be bred together.

That is the great danger of breeding with Merle tigers. Breeders who do not want to miss the unusual coat color avoid the risk of breeding seriously ill puppies with a special trick: in order to have Merle puppies in one litter, they mate a dog that carries the diseased gene with a dog who is genuinely healthy.

This means that half of the offspring are merle-colored (heterozygous) and half are brown (homozygous). Thus, one deliberately breeds the merle color without the risk of sick puppies. In view of the dangers involved in breeding Merles, this tactic should also be viewed critically. You will find out why in the next few sections.

The health risks of the merle factor - possible diseases

The great danger of the gene is revealed when a young animal is born that carries the factor genetically. Various eye diseases such as the formation of cracks in the eye membranes (coloboma), greatly reduced eyes (microphthalmia) or rounded pupils (dyscoria) are the result. Most of the puppies are blind, sometimes even deaf. In various cases, in addition to the very common malformations of the eyes, deformations of the skeleton or the genital organs and even the heart occurred.

Puppies that are born with a pure merle color show a reduced zest for life and often die before sexual maturity.

Various studies have created a rule of thumb how to identify a Merle piebald: as soon as more than 50% of the fur is colored white, the dog usually carries the defective gene genetically. But as is usually the case in nature, you cannot of course rely 100% on such rules. There are also “hidden merles”.

But not only the poor “products” of irresponsible breeds struggle with the beauty craze - the mixed-blooded animals that wear the well-known Merle color can also be adversely affected by the genetic defect. Some of the colored dogs have problems with their balance, which is particularly evident when swimming. Here the animals have a considerable disadvantage compared to healthy conspecifics. This problem is due to the fact that melanocytes can be found in the inner ear, which is responsible for the sense of balance. These cells are heavily pigmented and are thus changed by the genetic defect. Tests on the hearing ability of the Merle animals came to a frightening result: even 37% of the apparently healthy piebalds suffer from hearing impairments. In general, an increased mortality of the affected young animals was also found.

How dangerous is the defect for health?

Basically, a Merle piebald can lead a completely normal, largely unrestricted life. If each of these dogs had obvious health problems, the Merles would certainly not have achieved the level of popularity they have today.

The fact is, however, that there is a risk of dramatic illness and should not simply be ignored. Keeping these animals harbors some dangers, especially in the hands of more or less informed private individuals. It happens too quickly that a possibly ignorant animal lover comes up with the idea of ​​mating his handsome Merle male with the Merle female across the street. In some circumstances, very sick young animals are born that are difficult to convey due to their illness. Instead of getting a few euros for the lovely puppies, as hoped, you have to turn to animal welfare and ask for help in the worst case to iron out these faux pas again. In addition, you have to deal with your own conscience of causing suffering.

Even if you find out something on the Internet, you are not immune from the danger of becoming a torture breeder yourself. The information that you shouldn't pair two dogs with a Merle check can be found quite quickly when you google. Unfortunately, the matter is not that simple, because there are still the "hidden" Merle colors. There are three variants by which the dog cannot be recognized as a merle, even if it has the corresponding mixed-hereditary genetic makeup.

On the one hand there is the so-called cryptic merle. In this variant, the aforementioned SINE insertion is so short that the malformation of the pigment is not reflected in the external appearance of the dog. The animal can look like a normal black Australian Shepherd, but still carry the explosive genetic material. In the worst case, he will be paired with an obvious Merle and a litter of thoroughbred Merle puppies will result. There is also the phantom merle. They too look like solid colored healthy dogs. However, their genetic makeup is mixed. If necessary, however, the spotting is superimposed with naturally white regions in the fur. So you think it's a healthy dog.

Finally, there is another gene that affects color and, when combined with the merle factor, creates a dangerous mix. The so-called e-locus, which is located in a different location in the genome than the SILV gene, can turn the dog's coat yellowish if the trait is genetically pure. The yellow color is due to the fact that only pheomelanin is produced in the dog. If you have paid close attention, you can now draw the link between the e-locus and the merle color: Since the SILV gene only affects eumelanin and there is no eumelanin in a yellow Australian Shepherd, the defect in the SILV gene is not to recognize. With the Australian Shepherd, this shouldn't be too much of a problem, as the color yellow is undesirable in this breed and so probably no breeder would think of breeding with such a dog. However, since both the genetic defect and the e-locus occur in many other breeds that tolerate both coat markings, there is a great risk that a normal merle will be paired with an unrecognizable one. The result: sick puppies.

What does the Animal Welfare Act say about the merle factor?

In Section 11b (1) of the Animal Welfare Act it is “forbidden to breed vertebrates [...] insofar as [...] breeding findings [...] suggest that as a result of breeding [...] in offspring [...] hereditary body parts or organs for the species-appropriate use is missing or unsuitable or altered and as a result pain, suffering or damage occurs ”. These conditions are given with the Merle factor, at least if a pure-breeding agent is produced, which with a probability of 50-100% will be born disabled. That is why breeding with Merle piebalds is prohibited by the Animal Welfare Act.

However, this prohibition does not cover crossing a mixed-blood merle tiger with a dog without the defect. Therefore, the breeding of Merle piebalds is still carried out in this way by various breeding associations and is seen as permitted. However, if you look at the so-called Qualzucht report of the Federal Ministry of Food and Agriculture, the world looks very different. In this report, the ministry makes a recommendation on how Section 11 of the Animal Welfare Act should be interpreted and which prohibitions should result from it.

Various hereditary diseases of the dog are discussed, including the "Merle syndrome". In the report, the BMEL clearly speaks out against general breeding with Merle tigers, since health risks must be expected even with mixed-breed carriers. Although this statement is to be seen more as a recommendation than an order, more importance should be attached to this report.

vetevo conclusion

The question of whether one should support merle breeding inevitably arises in view of the previously described dangers for the pretty piebalds. Once again it is up to you yourself. With a lot of care, in-depth research and sufficient judgment, you can form your own judgment about the Merle factor.

This beauty has its price. And not insignificant: because it is about the health of the dogs. Ultimately, you have to choose between an unusual dog with a genetic defect and a healthy dog ​​without a check. Anyone who wants to breed their own litter of puppies as a hobby breeder has to be clear about one thing. The pairing of a merle with a merle falls under torture breeding and is prohibited according to the animal welfare law. We hope that with this text we were able to give you food for thought on the subject and reveal the secret of the bright blue eyes for you.

vetevo - out of love for animals.

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