Breeding with carrier – why not?

 

Genetic tests in dog breeding - it is becoming more extensive and unfortunately always more confusing for the breeders.

JME, DM, dilute factor, EOAD, Haemophilia ... all these are keywords that hit us on the websites and on Facebook.

How to deal well with the results of genetic testing is the difficulty and the great challenge of our time.

As far as genetic testing is concerned, our breed is still in its infancy right now. Over the next few years, a lot of new tests will certainly be developed and we need to learn to deal with these results reasonably, not to pour out the "kid with the bath," as the saying goes.

 

Usually one hears from the breeders just "I only take a stud dog who is free in all genetic tests ..." or "I am not going to get it through a carrier ...".

However, we can not see the whole thing in such a black and white way, because it is not that simple - even if it seems that way in the first instance.

Our gene pool will be severely restricted if we limit ourselves to a few breeding animals, which are of course than used excessively.

Genetic tests are becoming increasingly important for breeding, but to exclude carrier dogs from breeding in general is breeding stupidity.

For a better understanding, we must first go into the inheritance of a recessive gene in more detail.

What is an Autosomal Recessive Inheritance?

Autosomal recessive inheritance is a form of heredity in which the defective allele must be present on both chromosomes for the disease or trait is pronounced. Only homozygous carriers of the affected allele become ill.

Take, for example, the juvenile myoclonic epilepsy (JME), which has been talked about a lot in recent months.

When the genetic test is performed, there can be 3 different results:

N / N - free from JME
JME / N - carrier of the defect gene
JME / JME - affected for JME (at risk/sick)

That means, that a dog that has been tested N / N does not carry the defect gene and therefore can not pass it on. 

A dog whose result is JME / N carries the defect gene but will never get ill on this sickness. But it also means that he can pass on this defect gene to his offspring (statistically 50/50) and therefore also needs a breeding partner with the result N / N, so that none of the offspring get sick.

JME / JME is the gene status of diseased animals. By no means we should breed with dogs with this gene status.

 

To sum up:
A dog carrying one allele of a diseased gene will never get sick! With a clear test breeding partner he will never produce sick progeny! 

 

What does that mean for the breeding?

An example for illustration:

A male dog is used by many breeders as a stud dog because he is free in all genetic tests that are currently available.

A few years later, a new gene is discovered that is responsible for a disease, and also a new test is developed. The male, who was previously free in all genetic testing, is now the carrier for this newly discovered gene.

Then we have the situation, that this male of course has given this defect gene to a large number of his offspring.

Another male, who proved to be a carrier in one of the then possible genetic tests in former time, was never used for breeding by the breeders because of this result. However, this male is free tested on this newly discovered gene, and now ...?

In the worst case, this bloodline is lost for our breed, because the male is then too old and can no longer produce offspring. And that only because the breeders lacked foresight.

This example shows that we have to be very careful with genetic testing.

Excessive use of the same stud dogs is by no means sensible and dangerous, because the more tests are developed, the greater the likelihood that each and every one of our breeding animals will eventually be tested for any gene as a carrier.

If we are breeding so narrow minded, then we have no more breeding dogs at the end.

If we are so narrow-minded in our breeding, then we have no more breeding dogs at the end.

 

Carrier dogs are also authorized in breeding and for genetic diversity it is important not to ignore this!

Of course, they may only be paired with breeding partners who have been freely tested in this genetic test, so that no animals  are bred who are affected by this disease.

But for diseases with a recessive inheritance, for which there are already genetic tests, that is also quite simple.

We must guard against branding entire bloodlines due to the fact, that some dogs in these lines have been tested as carriers. In some diseases the lines are known and certainly should not be doubled, but it must not cause that in principle certain lines are no longer used in breeding, because that would narrow our genetic bottleneck even more and will lead to other problems , 

 

 

The breeders' thinking over generations - not just from one litter to the next - that's the big challenge - that has always been it and it always will be. Genetic tests can help us in breeding, but they are not the only remedy. 

Reasonable used they are a great help for us today and in the future, in order to advance the breeding of healthy dogs.

 

Monika Pehr
March 2018