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Precious genes – why is the diversity of genes so important to our dogs?

By Evelyn Kirsch
Translation into English Rosalind Priest

In recent years, the call for a broad gene pool in dog breeding is getting louder. Geneticists repeatedly warn against the dangerous path of closed dog breeding. But why? We just want to breed the best. It cannot be wrong if only the best breed representatives are used in the breed. Where is the problem?

Dog breeding has been geared primarily towards improving the breeds for the past one hundred years or at least trying to maintain the high level that has been achieved. This was done by carefully studying pedigrees; only the best specimens could be found in it. Health, nature, athletic ability and the excellent standard features, that’s what we want. We make sure that only particularly well-known representatives of our breed in the pedigree are available. And blood connection must necessarily be found. Just before warn the geneticists. Why – what’s wrong with that?

What we are looking for with this type of selection is only a very small part, which is determined by the genes. The genes have many other tasks. For example, they are also responsible for the body’s ability to deal with temperature fluctuations; they are responsible for keeping the immune system strong or also for the ability of a dog to deal with stress, etc., etc. These skills can be lost and are already greatly reduced in many breeds. Our breed of dogs leads to increasing problems such as allergies, cancer and other so-called civilization diseases. But why is it like that?

Homozygothia or mixed heterozygosis
For more than a hundred years of breeding, our breeds have become much unified. Most races are clearly different from other races. The winners at exhibitions look very similar and performance dogs have become the fastest and most skilled. We have come to these successes because over these many years the gene pool of our dogs has become more and more pure. So-called racial errors have been pushed back so far by the selection that in most cases they no longer occur in the gene pool of a breed. We have lost it. “That’s a good thing,” it says. But who knows what we have lost, what we cannot measure directly or recognize so quickly. A recommendable reading on this subject is the book “Breed Breeding Genetics for Breeders and Holders” by Irene Sommerfeld-Stur. It explains in detail the current state of science, how genetics works and what options we still have to get the existing gene pool and not lose even more of the useful genes.

It is well known that in each individual’s gene pool there are dominant and recessive aleles for each trait. Each property (except the sex cells) is duplicated in the gene pool. In an example, this principle is explained quite simply: flow. Brindle is dominant and untreated recessive. Because brindle is dominant, we do not see from the outside whether the individual is purebred or mixed-breed brindle. Therefore, if we pair a brindle male with a solid bitch, the direct offspring will also be brindle, provided that the male is homozygous for the genome, but they also carry the recessive gene for the mother unaffected. But if the male carries both a dominant gene for flow and a recessive gene for solid (heterozygous), then all the direct offspring will mathematically be 50% brindle and 50% solid with the emphatic partner. In these 50% unscreened offspring the gene flow is lost. So we could, if we like, eliminate the gene flow very quickly within one generation of our race population, if we exclude all brindle dogs from the breed. (Unlike dominant genes, it is recessive, where a gene – if any – could only be grown from the gene pool if it can be identified by a genetic test.)

Loss of genetic diversity – a danger
The fact is, we can lose properties irretrievably. Let’s also think about the problem with the pug. By very strict selection he lost his nose – she has irretrievably disappeared from the gene pool of the breed. Only by crossing in an alien race could you feed it again. That was certainly not wanted by the breeders.

Well, we sight hound friends are far from practicing tormenting. But even our dogs have something to lose. Without wanting to do so, the diversity of genes is lost through our breeding selection and this can even be very dangerous. Is that true? Why can’t we do without all these genes, which were succinctly referred to as “filler” genes.

Science is already well advanced in genome research. It is already understood a lot. In the body of a living being very complicated functions and processes take place, in which very different genes are involved. Genes show very different compositions, functions and properties. The functioning of a body involves a vast array of biochemical effects and interactions governed by genes and the environment. The dog consists of fur, eyes, ears, teeth, skin, muscles, tendons, nerves, blood vessels and not to forget the internal organs. All these parts are made of different fabrics and are brought to work together by various forces. Ultimately, it is the cells that form the foundations that are again made up of the smallest building blocks, such as the cytoplasm, cell nucleus, mitochondria, etc., etc. The kit of all items is found in the DNA, which is packed in the nucleus. The DNA is reminiscent of the structure of a rope ladder, it consists of sugar, phosphoric acid and various bases. It is very complicated to understand how all these mechanisms work together. But we know that the functions of the body are controlled by proteins, among other things. There are enzymes, hormones, immunoglobulins, membrane receptors and neurotransmitters. The different proteins are in constant collaboration and interaction with each other.

Genes are information units that contain the assembly instructions for proteins. They lie in pairs in one place, the so-called gene locus. The two genes at a locus are called aleles, each one allele is from the father one of the mother. Both alleles can be identical (homozygous or homozygous) or different (heterozygous or mixed). Different alleles of a locus encode proteins with more or less different structure or different function. When we think of the example of flow, it is obviously not important for health and vitality whether a dog is brindle or solid. However, there are also many genes with more important functions, e.g. affect the health. There are z. B. Defective genes where the disease-causing allele is naturally undesirable. But there are also genes where both alleles, if they are different, also have desirable different properties.

Inheritance errors only have a chance of harming the dog if they are homozygous, so having a variety of genes helps prevent these mutations from hitting each other and making our dogs sick.

 

Useful genes – how do they work?
As an understandable example, Ms. Sommerfeld-Stur mentions in her book mentioned above: “On the individual level, a dog carrying different variants of a gene has the advantage that it always carries at least one suitable variant of the gene for different environmental conditions. Take a hypothetical example. An enzyme responsible for delivering energy to the workings of the musculature exists in two variants, which differ in their temperature sensitivity. Variant A works best in a body temperature range between 36.5 ° and 38.2 °, variant B has its environmental optimum in a temperature range between 37.4 ° and 39 °. Both enzyme variants lose activity when body temperature rises above or below their individual optimal range of action.

In a dog that is homozygous for variant A, the enzyme and thus the energy supply of the muscles will work as long as its body temperature does not rise above 38.2 °. In mild fever, this dog will show a more or less pronounced weakness of the muscles. A dog homozygous for variant B, on the other hand, will respond with muscle weakness if hypothermia lowers its body temperature to below 37.4 ° C. The best cards have a heterozygous dog that has both variants of the enzyme”.

Another example showing how valuable heterozygotes are is described by them as follows: “But even simple dominance effects explain the superiority of higher heterozygosis. Recessive genes in most cases encode ineffective or less potent proteins. Thus, animals with a higher proportion of heterozygous gene loci have at least one copy of the dominant gene coding for the functioning variant of the gene product at more loci, while animals with a higher proportion of homozygous loci also have a higher proportion of recessive genes or code missing function, carry in double dose”.

Very important genes, which are mainly responsible for the field of immune defence, are the genes of the MHC (Major Histocompatibility Complex) they are referred to as DLA genes. (DLA stands for “Dog Leukocyte Antigen”). These genes come in three classes and are very well studied. There are several genes involved in which sometimes very polymorphic genes are described with many alleles. Alleles of these three loci are often inherited in certain allele combinations, also referred to as haplotypes. More than 144 such haplotypes have been found in more than 80 breeds.

Scientific findings
It has now been found that in individual breeds this diversity is already greatly reduced. Ms. Sommerfeld-Stur describes that in the case of the “Boxer” and “Golden Retriever” in the DLA I gene of the 51 alleles known in the dog, only 10 more alleles could be found. “…” Of the total of 144 haplotypes, the majority are of affected breed dogs can only find more than 2 to a maximum of 4 different species. “The immense loss of these so-called haplotypes in the affected breeds increases the risk of acquiring the civilization diseases known today, such as diabetes or the various autoimmune diseases.

The loss of these alleles occurs through homozygosis at homozygothia at the respective loci where the various alleles have different roles. That’s the price we pay for fixing the desired standard and performance requirements through homozygothy.

A well-known danger that we have often discussed in pedigree breeding is the phenomenon of “popular sire”. Particularly successful stud dogs, which also have successful offspring, are used immensely in breeding. We already know that this can lead to the fact that a defect gene, which the corresponding male possibly carries, can spread thereby explosively in a breed. But there is also another danger. If we use only the few super winners, other dogs stay out. But just these, could have valuable genes that no other breeding dog of this breed possesses. As a result, a valuable property could be lost forever.

Only the best in the breed?
That shows us that we have to rethink. For geneticists, our strategy of “only the best in the breed” is a fatal mistake. We would rather work on the strategy of “just the worst off the breed” to get our precious gene pool.

Breeders should not only think in their own breeding lines, they should think in the population. Over the many years of selection breeding we have already lost a great deal of genetic diversity. We should now do our utmost to preserve the existing as complete as possible. (And we still have a big advantage in some of the greyhound breeds: we can / could still rely on specimens from the country of origin with a very different gene pool.)

Through continued generations of breeding and line breeding our dogs are threatened by an inbreeding depression. The inbreeding depression, which leads to less and less fitness, vitality and fertility, is driven by the increasing number of homozygous defect genes. Defective genes are for the most part recessive. They can’t be recognized as long as they are in mixed form. So they can be present in our race for a long time without being noticed. However, they will appear due to the increase in the purity. We are then faced with a long-standing problem that is very difficult to control.

A well-filled toolbox
In order to keep our dogs as healthy as possible, we must, in addition to the long-known breeding strategies; preliminary examinations, etc. also pay attention to heterozygosis. Today we know that genetic diversity can be compared to a toolbox. With the large number of different genes and gene variants, an organism has more opportunities to respond more effectively to environmental hazards because of a wider choice. The more different genes, the more tools that may then act more specifically. You can also get a nail with the handle of a screwdriver in the wood, if no hammer is available. The hammer is definitely the most effective tool for this job. The choice makes it. We have the task to give our bred dogs a well filled toolbox.

In the future, we should supplement our selection criteria such as health, nature, athletic ability and excellent standard features, namely the genetic diversity.

Reference: RASSEHUNDEZUCHT – GENETIK FÜR ZÜCHTER UND HALTER von IRENE SOMMERFELT-STUR