A "short" lesson on Genetics and health testing

Genetics is not a topic that is easily understood by the masses and sometimes not even understood by breeders! I’m going to try to do a basic genetics lesson that is as easy to understand as I can make it. There is MUCH more involved but for the purposes of the points I need to cover in the way I breed dogs in regards to known and testable diseases I’m going to only hit the high points. Many of the issues that we have genetic testing for are caused by mutations in a single gene. If the condition is known as being “dominant” than a single copy of that mutation can be inherited by only one parent and will cause a dog to be “affected” by that mutation and show the traits or disease involved. A mutation that is “recessive” means that in order to be “affected” the dog must inherit two copies of the mutation, one copy from the mom and one copy from the dad. In the case of a recessive mutation, if a dog only has one copy of the mutation than the dog is known as a “carrier”. A carrier does not show the traits or disease and is perfectly healthy. If a dog does not have any copies of a mutation than they are known as “clear”. Most of the conditions involved in our breed that have a test are Recessive.

When it comes to breeding in the case of conditions that are known to be RECESSIVE the following matches will produce the following results. The picture included shows this also for those that like visual examples.

Clear X Clear – This is obviously the preferred type of breeding because no puppies will ever be affected or carry even a single gene for the disease in question.

Clear X Carrier – 100% of puppies produced will be free of the disease. Each puppy produced will have a 75% chance of being Clear and a 25% chance of being a Carrier. 

Clear X Affected – 100% of puppies produced will be free of the disease. However, every puppy produced will be a Carrier.

Carrier X Carrier – Each puppy produced will have a 50% chance of being a Carrier, 25% chance of being Clear, and 25% chance of being Affected.

Carrier X Affected – There will be no Clear puppies produced. Each puppy produced will have a 50% chance of being a Carrier, and a 50% chance of being Affected.

Affected X Affected – 100% of puppies produced will be affected by the disease. This breeding is not recommended. However, in the case of rare breeds with diseases that are not life threatening, this breeding could be done and then offspring could be bred out to a Clear individual, producing puppies that are Carriers. Those Carriers could then be bred to a Clear partner and a Clear offspring could be kept to carry on the lineage and desirable traits of the affected dogs while eliminating the mutation for the disease in question.

Ethical Breeders do DNA testing to try and eliminate diseases that their breed is known for. They pride themselves on having all clear individuals in their program and that is great! DNA testing has come a long way and is a very helpful tool for creating healthier dogs in the future if used appropriately. Unfortunately, many breeders will completely remove an individual from their program based on the status of a dog instead of working towards eliminating the disease while keeping what is known as “genetic diversity”. All breeds have a limited amount of genetic diversity because most breeds were developed using a smaller number of dogs. Every time a new DNA test is developed for a disease to determine the genetic status of each dog, the gene pool shrinks because breeders will eliminate dogs from their program. While every good breeder’s goal is to produce healthy puppies, what many of them forget is that they are also eliminating the many good genes that dog carries. They are essentially “throwing the baby out with the bathwater”. The problem with this, is that over time, since all of those good genes were thrown out with the bad one, new mutations are more likely to pop up and will be harder and harder to breed away from.

If a mutation is a serious, life threatening or debilitating disease I can understand the knee jerk reaction to cut that from a breeding program. Unfortunately, many breeders are doing the same thing with low level diseases that do not greatly affect the life of the dog which narrows our gene pool and is detrimental for the future. Luckily, I have not been faced with that decision and have only dealt with issues that were non-life threatening or easily fixed with today’s medical advancements. In the past I have always tested my stud dogs for MAC & Myotonia Congenita, two Recessive diseases. Knowing my stud dogs are clear, I can breed to any female and know that I will not produce Affected puppies that could be sick. Since all my puppies are placed with non-breeding agreements, that is perfectly acceptable. 

With the 2020 addition of Embark DNA testing the same holds true. While I am working towards having all Clear individuals, I do have some that are Carriers. Being Carriers, they do not actually have the condition and the condition that they carry for is not debilitating to the dog. I am not going to throw out the good things that I want to keep from these Carriers and will be breeding to Clear dogs. If you refer back to the top or to the color coded chart below, you can see that all puppies will be unaffected by any DNA testable disease. In the rare event that a breeding would be done between individuals that could produce an affected puppy, the whole litter will be tested before placement and any puppy that would test Affected would either be retained here at Belle Vista or placed with full disclosure of the condition. 

For the Miniature Schnauzer breed, there are really only a few things that we have genetic tests for: Myatonia Congenita, MAC (Mycobacterium Avium Complex), PMDS (Canine Persistent Müllerian Duct Syndrome), PRA-B HIVEP3, and Factor 7 Deficiency (rare in the breed). While I use and like the Embark DNA testing (there are other companies doing the same thing), they test every dog for everything; shooting out a report that says they are clear of 190+ diseases. The problem with this is that 187 of those were developed for different breeds and have absolutely no bearing on the Miniature Schnauzer. Even if the Miniature Schnauzer and Australian Shepherd are both prone to Inherited Cataracts, the same mutation does not cause it. So the test will say that the dog is free of Inherited Cataracts because the test was developed for an Australian Shepherd but that could be false because the mutation that causes Inherited Cataracts in the Miniature Schnauzer hasn’t been discovered yet and there is no test. So some breeders tout things like “Tested clear of 190 inherited diseases!” to make their dogs and breeding program sound superior. While it isn’t a lie, it is false marketing for the general public that does not understand how genetic testing works. As science advances more and more tests will be available for the breed but until then, many of the things we deal with have no tests. 

Breeders must have awareness of what the puppies they produce experience and the only way they can know is with the help of their puppy families keeping them updated. One dog experiencing an issue can be a fluke but multiple reports from people with related dogs points to an issue and the breeder needs to use due diligence to try determining the culprit in the pedigree and remove it from breeding. This can be difficult because if the issue is a recessive issue, it could have ridden through multiple generations as a “carrier” before then getting doubled up on to produce affected offspring. Breeders also need to keep perspective on what type of issues create a problem big enough to cut good genes with the bad. Anything that causes death, greatly reduces the quality of life, or produces a hardship for the owners should be scrutinized and removed if possible.