Why DNA Testing Won’t Necessarily Lead to Healthier Dogs

Why DNA Testing Won’t Necessarily Lead to Healthier Dogs

Breeders of purebred dogs are faced with a conundrum. By striving to produce dogs possessing consistent and reproducible physical characteristics through line-breeding, they may be losing genes important for the dog’s basic function and health. When the practice of line-breeding is combined with the practice of eliminating dogs from their breeding program based on the results of DNA testing, you have a formula for disaster.

In this post, Carol Beuchat, PhD, vertebrate biologist and founder of the Institute of Canine Biology, explains why the use of DNA testing when making breeding decisions won’t necessarily result in healthier dogs. This post builds on a previous Healthy Dog Blog post by Dr. Beuchat entitled Using Genetics to Breed Healthier Dogs.

While it is true that genetic testing can prevent producing offspring with specific genetic disorders, genetic testing is not the way to healthier dogs. All dogs have recessive mutations (and so do we), and these little genetic accidents cause no harm as long as an animal has a copy of the normal gene. So we can pass these harmless DNA errors on to offspring just like any other gene, usually with no consequences because any particular mutation should only occur in just a few animals in a large population. But if an animal should happen to get two copies of a mutated gene, the normal gene is absent and whatever that gene is supposed to do won’t happen -a step in development, the production of some enzyme for digestion, a fatty acid needed to form cell membranes, a hormone to start lactation – the mission of that gene is thwarted and the animal has a genetic disorder.DNA

Now, enter the breeder, who wants to breed for particular traits in their dogs. The easiest way to do this is to breed dogs that have those traits, and even better if the dogs are related so they have the same genes. This will make litters more uniform and increase the chances of getting the puppy you want with all the right traits. Inbreeding and line breeding are the tried and true ways to do this.But all dogs have mutations, and breeding to get the good genes from a relative will also give you the bad ones. Breeding to dogs with the same genes will produce puppies that are homozygous for those genes, whether they are good or bad. This is why genetic disorders in purebred dogs are increasing: as they become more inbred (more similar genetically), the chances of getting two copies of a mutation will increase. There’s no way around it; it’s just math.

So here’s the conundrum. Breeders should test their dogs for known mutations, so they can prevent producing puppies that will suffer from those disorders. But if after all testing is done, the breeder selects as a mate a closely related dog, they have eliminated the risk of one disorder that is known, and substituted a risk for a disorder that is unknown. Doing your DNA testing religiously then inbreeding is working at cross-purposes, and the closer the breeding the higher the probability you will get some problem that you really don’t want.

So the road to breed health is not genetic testing. DNA testing alone will not – cannot – make dogs healthier. Breeding practices that increase homozygosity – breeding to close relatives, will relentlessly, unavoidably, and inevitably destroy the health of the purebred dog. There’s no way around it; it’s just math.

Carol B ICBCarol Beuchat, PhD is Founder and Scientific Director, Institute of Canine Biology (www.instituteofcaninebiology.org ) and member of the Department of Molecular and Cell Biology, University of California Berkeley. To connect with Carol on facebook go to: www.facebook.com/#!/carol.beuchat.9?fref=ts


Using Genetics to Breed Healthier Dogs

Using Genetics to Breed Healthier Dogs

Chromosomes with copyCarol Beuchat, PhD, vertebrate biologist and founder of the Institute of Canine Biology, is passionate about using information obtained through canine population genetics to breed healthier purebred dogs. Population genetics is defined as the study of allele frequency distribution and change as a result of evolutionary processes. In simpler terms, it is the study of changes in genetic diversity that occur both naturally over time and as a result of selective breeding. Carol is motivated by the increasing number of genetic disorders in dogs and is working with breeders to use population genetics to breed healthier dogs and to limit contraction of the gene pool of purebred dogs. Carol offers virtual classes on population genetics through facebook, so if you are interested, connect with her there. She recently summarized her thoughts on why an understanding of population genetics is so important.

1) All the useful genetic variation your breed will ever have was in the dogs that founded the breed. This genetic diversity is finite.

2) Every generation, alleles are lost by chance (genetic drift) and also by artificial selection by breeders who select for dogs with the traits they like and remove other dogs from the breeding population.

3) Because the stud book is closed, genes that are lost cannot be replaced.

4) So, from the moment a breed is founded and the stud book is closed, loss of genetic diversity over time is inevitable and relentless.

5) You cannot remove a single gene from a population. You must remove an entire dog, and all the genes it has.

6) You cannot select for or against a single gene, because genes tend to move in groups with other genes. If you select for (or against) one, you select for (or against) them all.

7) Breeding for homozygosity of some traits breeds for homozygosity of all traits. Homozygosity is the kiss of death to the immune system. And as genetic variability decreases, so does the ability of the breeder to improve a breed through selection, because selection requires variability.

8) The consequences of inbreeding (in all animals) are insidious but obvious if you look – decreased fertility, difficulty whelping, smaller litters, higher puppy mortality, puppies that don’t thrive, shorter lifespan, etc. Genetically healthy dogs should get pregnant if mated. They should have large litters of robust puppies, with low pup mortality. Animals that cannot produce viable offspring are removed by natural selection.

9) Mutations of dominant genes are removed from the population if they reduce fitness. Mutations of recessive alleles have no effect unless they are homozygous. So rare alleles are not removed, they are inherited from one generation to the next, and every animal has them. Lots of them.

10) If you create a bunch of puppies from your favorite sire, you are making dozens of copies of all of the bad alleles in that dog (which were never a problem before; see 9) and spewing them out into the population. Now, a (previously) rare mutation will be common, its frequency in the population increases, and the chances go up that some puppy will be produced that is homozygous (has two copies of that bad allele) and homozygous recessive alleles are no longer silent.

11) So, genetic disorders caused by recessive alleles don’t “suddenly appear” in a breed. The defective gene was probably there all along. Make a zillion copies, and you have a disease.

12) Using DNA testing to remove disease genes will not make dogs healthier (see 2, 5, and 6).

13) The breed will continue to lose genes (by chance or selection) until the gene pool no longer has the genes necessary to build a healthy dog.

14) At this point, the breed might look wonderful (because of selection for type), but will suffer from the ill effects of genetic impoverishment (inbreeding depression, diseases caused by recessive alleles, increased risk for cancer, etc).

15) The only way to improve the health of a breed is to manage the health of the breed’s gene pool.

16) The health of individual dogs cannot be improved without improving the genetic health of the population. Population genetics provides tools for the genetic management of populations, and breeders CAN improve the health of the dogs they breed if they understand and use them.

CAROL BCarol Beuchat, PhD is Founder and Scientific Director, Institute of Canine Biology (www.instituteofcaninebiology.org ) and member of the Department of Molecular and Cell Biology, University of California Berkeley. To connect with Carol on facebook go to:https://www.facebook.com/#!/carol.beuchat.9?fref=ts


The Only Difference is What Their Mother Ate!

The Only Difference is What Their Mother Ate!

MiceIt takes more than good genes for good health. This point is dramatically demonstrated in this short video showing two mice from the same mother, but different litters. The two mice are genetically identical, have eaten the same diet since birth, and were raised in exactly the same environment. The only difference is the diet the mother ate during her pregnancy! Not only do these mice look different, but along with being obese, the yellow one is at higher risk of developing diabetes and cancer. In contrast, the brown mouse is leaner and less likely to develop these diseases.

The effect of environment on gene expression is called epigenetics. Genes can be likened to computer hardware and epigenetics to the software. Put another way, DNA has the instructions; epigenetics is how those instructions are read.

The importance of epigenetics goes beyond diet. Chemicals from our environment as well as chemicals produced by our bodies bind to our DNA every second of every day and affect how our genes are read. These chemicals determine if the gene is turned on or off – they even determine how much it is turned on. This is why we at arf think that good nutrition, minimizing exposure to potential toxins (including vaccines, medications, and environmental toxins) and joyful living are so important to achieving and maintaining good health.