Carol Beuchat PhD
Many breeders stress that the key to improving canine health is DNA testing and selective breeding, and many national kennel clubs and breed clubs endorse this view. However, the evidence does not support the claim that this strategy will prevent genetic disorders or even improve the health of dogs. In fact, it is easy to show why this will not work based on simple principles that any breeder can understand.
Let's say we start with a small population of healthy dogs that are not related to each other. Let's put them on an island and allow them to breed freely for many generations. Over time, individuals in the population will become more and more related to each other because of the limited number of individuals to mate with. Just by chance or through selection, some alleles in one generation will not get passed on to offspring in the next generation and will be permanently lost from the gene pool. At the same time, unavoidable inbreeding will increase the level of relatedness among the individuals. The net effect is that some individuals will have two copies of a dysfunctional allele at a locus instead of at least one copy of of the normal, "wild-type" allele.
The replacement of normal alleles with mutations will results in a decline in health and "vigor", including both genetic diseases and measurable traits such as reproductive success, lifespan, and survival. At this point, the population can be considered to be unhealthy, and the problem is the erosion in the quality of the gene pool.
The replacement of normal alleles with mutations will results in a decline in health and "vigor", including both genetic diseases and measurable traits such as reproductive success, lifespan, and survival. At this point, the population can be considered to be unhealthy, and the problem is the erosion in the quality of the gene pool.
If this was a dog breed displaying some health issues, we would assume the problem is genetics and start looking for a mutation. Sometimes one is identified, but more often the situation appears to be complex and we are unable to identify a clear cause among what we assume is a background of polygenic effects.
We have had only very limited success dealing with problems like this. There is no easy way to select against multiple unknown genes, so usually animals are removed from the gene pool. But this rarely solves the problem. New animals similarly affected continue to appear, sometimes stimulating more research to find the offending mutations. Ultimately, the solution often becomes the removea of animals from the gene pool once again.
We have had only very limited success dealing with problems like this. There is no easy way to select against multiple unknown genes, so usually animals are removed from the gene pool. But this rarely solves the problem. New animals similarly affected continue to appear, sometimes stimulating more research to find the offending mutations. Ultimately, the solution often becomes the removea of animals from the gene pool once again.
After decades of engaging in similar strategies, breeders have not eliminated any of these problems, except where caused by a single recessive or dominant mutation. Why is this?
We identify the problem as "bad" genes we have to get rid of. Rather, it's not the bad genes that are the problem, it is the LOSS of the normal, functional genes that should be found at that locus. They, of course, are lost through genetic drift and selection with each generation of breeding. If every unique allele in a breed's gene pool was passed on to an animal in the next generation, then the composition of the gene pool would be stable over time, and we should be able to produce healthy, quality animals generation after generation. But we don't breed in a way that protects the contents of the gene pool. Thus alleles are lost every generation, either by design or by chance. We do not protect the genes that are necessary to produce healthy animals, so as they disappear from the gene pool, we have to expect that we will see problems.
Interestingly, most wild animal populations can persist for hundreds of years, maintaining health and function because the complement of genes necessary to produce the animals is constant. How do these unmanaged populations of animals do this? It's simple. The alleles that are lost are replaced when new individuals join from other populations. This is also done deliberately in commercial animal breeding, when a single population is subdivided and managed in a rotational breeding program. This practice restores genes lost from one subpopulation through the introduction of animals from another subpopulation. A carefully run program can continue to breed in a closed gene pool for many generations, simply by preventing the loss of alleles from the gene pool. The valued traits of the animals are preserved and the health and quality of the animals are maintained at a high level.
Note that the gene pools of ALL animals contain mutations. Why don't these mutations result in the number and magnitude of problems we wrestle with in purebred dogs? The dominant mutations are removed if they have a sufficiently detrimental effect on the animals. Others will only cause issues if paired with another copy of the mutation, because the locus for this gene will have two copies of a non-functional gene. What is absent is a copy of the normal allele necessary for a particular function.
The problem isn't that the animal has a mutation; it's that it lacks a copy of the normal allele. Simply "getting rid" of the mutation will not solve the problem. The problem is not a malicious genetic bomb in the gene pool. It's the absence of the normal alleles that should be in its place.
What is critical for breeders to understand is that there is only ONE solution to this problem. It is to restore the alleles necessary to perform every function of the body of a dog. DNA testing will spot a few of the "bombs". But throwing those out still leaves a gene pool without the allelic diversity necessary to produce healthy animals. Every breeder knows from experience that trying to remove mutations by removing animals is fruitless; the result will not be a happy, healthy population of dogs.
Can you see that DNA testing to identify the few mutations we know about will not restore health to dog breeds? As long as the gene pool is closed, we cannot restore the gene pool to health and we will not be able to produce healthy dogs sustainably. If we want healthy dogs, we need to produce dogs with the complement of alleles necessary to support all the bits and pieces of function necessary to be a healthy dog. All breeds in a closed gene pool will already be suffering from a loss of alleles, some of which will result in loss of function. So, not only do we need to breed in a way that protects genetic diversity, we must take whatever steps are necessary to restore the diversity of the gene pools.
The problem isn't that the animal has a mutation; it's that it lacks a copy of the normal allele. Simply "getting rid" of the mutation will not solve the problem. The problem is not a malicious genetic bomb in the gene pool. It's the absence of the normal alleles that should be in its place.
What is critical for breeders to understand is that there is only ONE solution to this problem. It is to restore the alleles necessary to perform every function of the body of a dog. DNA testing will spot a few of the "bombs". But throwing those out still leaves a gene pool without the allelic diversity necessary to produce healthy animals. Every breeder knows from experience that trying to remove mutations by removing animals is fruitless; the result will not be a happy, healthy population of dogs.
Can you see that DNA testing to identify the few mutations we know about will not restore health to dog breeds? As long as the gene pool is closed, we cannot restore the gene pool to health and we will not be able to produce healthy dogs sustainably. If we want healthy dogs, we need to produce dogs with the complement of alleles necessary to support all the bits and pieces of function necessary to be a healthy dog. All breeds in a closed gene pool will already be suffering from a loss of alleles, some of which will result in loss of function. So, not only do we need to breed in a way that protects genetic diversity, we must take whatever steps are necessary to restore the diversity of the gene pools.
Our focus on DNA testing and selective breeding is failing to improve the health of dog breeds, and this is why. Advice to breeders that we can produce healthy dogs if we continue to use our current strategies is simply wrong because it suggests that loss of alleles every generation will have no detrimental effects on health and function. This is impossible.
There is lots we don't know about genetics, but there is nothing that would explain how we might continue to breed dogs as we are without the deterioration we are seeing in the health and quality of the dogs. In fact, the health issues that we wrestle with in purebred dogs are caused by the way we breed. To change the trajectory of declining health in dogs, we must change the way we breed.
The solution to our problem is obvious and conceptually simple. It has been practiced by breeders of other animals for many years. There is no magic necessary, and it's not hard. You do need good information and guidance from individuals that understand the details of population genetics in order to accomplish the genetic rehabilitation of a breed effectively and efficiently. The sooner you start, the sooner we can be dog owners and breeders without also being experts in cancer, epilepsy, kidney failure, or sudden cardiac death.
Finally, the average dog lover is growing intolerant of the high incidence of health problems in purebred dogs. They identify the breeders as part of the problem, and they are not wrong. Pressure on breeders to improve health doesn't seem to be resulting in significant improvement, so the impetus now is legislation that will regulate dog breeding and make it illegal to produce animals that can be expected to suffer from health issues.
Breeders have experience in dog breeding. We must pair this with expertise in the proper genetic management of animal populations. To restore dog breeds to health, we must encourage and support this essential partnership.
The solution to our problem is obvious and conceptually simple. It has been practiced by breeders of other animals for many years. There is no magic necessary, and it's not hard. You do need good information and guidance from individuals that understand the details of population genetics in order to accomplish the genetic rehabilitation of a breed effectively and efficiently. The sooner you start, the sooner we can be dog owners and breeders without also being experts in cancer, epilepsy, kidney failure, or sudden cardiac death.
Finally, the average dog lover is growing intolerant of the high incidence of health problems in purebred dogs. They identify the breeders as part of the problem, and they are not wrong. Pressure on breeders to improve health doesn't seem to be resulting in significant improvement, so the impetus now is legislation that will regulate dog breeding and make it illegal to produce animals that can be expected to suffer from health issues.
Breeders have experience in dog breeding. We must pair this with expertise in the proper genetic management of animal populations. To restore dog breeds to health, we must encourage and support this essential partnership.
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***************************************
Visit our Facebook Groups
ICB Institute of Canine Biology
...the latest canine news and research
ICB Breeding for the Future
...the science of animal breeding
