Inbred Mistakes III

Continuing the analysis of the pro-inbreeding essay over on the Absolut Bullmarket French Bulldogs site:

Many people believe that in breeding itself creates genetic disease. This is incorrect.

Again with a pointless strawman, as if putting out a statement that is easy to defeat will lend credibility to the rest of what she has to say.  A Google search for “inbreeding causes disease” returns only 6 results; apparently Carol believes this is a wave of ignorance taking over the world.  What is true, and what is really being argued even in those 6 poorly worded results on Google is better said, “inbreeding causes recessive disease expression.”

What is correct, however, is that inbreeding, by tightening the gene pool, increases the chances that recessive characteristics, including genetic diseases, will be expressed. A breeder may choose to do a tight line breeding to try to identify and remove potential carriers from their breeding pool. A breeder may also have two dogs, both of which have attributes which are very hard to come by in their breed – perfect angulation in a breed plagued with straight rears, fantastic breathing in a breed which tends towards airway impairments, or any other elusive quality a breeder wishes to capture for the future of their lines.

Again I must restate that inbreeding alone does not “tighten” the gene pool.  Inbreeding plus ruthless selection does.  Nor does tightening the gene pool by itself create recessive expression.  Increasing homozygosity does this and this happens as a result of inbreeding if you have ruthless selection or not!  If you inbreed on a recessive trait, you’ll get affected puppies.  If you keep all the puppies and breed them all equally, you haven’t done anything to tighten or shrink the gene pool.

The rest of her argument speaks to problems caused or exacerbated by a small number of founders, inbreeding suppression, or excessive selection.  The often used stinker is that somehow inbreeding is the solution to problems caused by inbreeding!  Well, in a way this is true just as Ebola is the cure for Ebola.  Eventually it kills you before you (and it) can reproduce and your inbred line dies out.  Sadly, this is not a breedwide, macro solution that we can tolerate.  The solution to inbred dogs should not be the extinction of dogs.

Another less pleasing possibility is the unfortunate habit of most puppy mills of simply throwing together the closest dogs at hand to produce puppies. Since it is not likely (let’s be honest and say it is impossible) that a mill will do what is required to ensure the offspring have no recessive defects, which is keep all offspring to maturity, this is definitely a situation to avoid.

Here we have a classical diversion.  Don’t mind my sins because the man over there is even worse!  Speculation about what puppy mills and “backyard breeders” do or don’t do has no bearing on the ethics and efficacy of inbreeding carried out by breeders.  Dog breeding is not a choose your own adventure book with only two choices: Inbreeding depression vs. Puppymill atrocities.  This is a false dilemma.

Intermittent inbreeding within a line or breed is not damaging to the long term health of the animals. However, inbreeding over successive generations can lead to reduced fitness and fertility problems among the offspring, resulting in a phenomena known as in breeding depression. It can take several generations to show up, depending on the traits involved.

This is misleading.  Inbreeding is both as dangerous and as effective in exact proportion to how much (successive generations) and in what way (how close) it is used.  It can not be more effective and less dangerous, those two traits are based on the exact same thing: the ability to double up on alleles. nThe danger of inbreeding, even just a little bit, is that a new mutation that would otherwise never be doubled up on will be doubled up on.

Let’s take a look at this example, based on an actual litter we produced:

Rebel Gambit Joe
Tara Spike
Roseanne Mark Frank
Tara Spike

In this case, the example shown is that of a half brother, half sister breeding. The dogs used share the same mother, but are out of different fathers. This breeding may be used again to try to identify and remove potential diseases from the breeder’s gene pool, or it may simply be a case of trying to ‘lock in’ an elusive breed characteristic which both siblings share, such as correct rear angulation. Again, I would expect to hear from the breeder, if I were a buyer, what their specific reasons were for doing this breeding. The plus is that the non appearance of genetic disease in the mature adults resulting from such a breeding are highly unlikely to be carriers of it, as well.

Here, Carol says that she wanted to double up on a full 1/8th (12.5%) of Tara’s genes in order to “lock in” “correct rear angulation.”  Is this worth the risks?  Most deleterious diseases are simple recessive mutations on a single allele.  This means that if Tara has one such bad allele, 12.5% of these puppies will be AFFECTED and 25% of the puppies will be Carriers.  And this is true, additively, for every single deleterious recessive Tara carries.

Is this worth it for a cute ass?  No one but a ribbon-chasing arm-chair platonist would think so.  Let’s give Carol the benefit of the doubt with this “elusive” characteristic and assume that it too is a simple recessive.  If it were dominant, we wouldn’t need to inbreed at all because we wouldn’t need to double up on this gene for it to be expressed.  If it’s a simple recessive and we also assume that Tara is doubled up on it, best case scenario, Rebel and Roseanne each are carriers.  Thus, 25% of the puppies will be doubled up, 50% will be carriers.  We only get 1 in 4 puppies with what we want, yet 1 in 8 puppies will be affected by any given recessive disease.  There’s only one gene we want, but there could be hundreds of recessive genes that we do not want, maybe thousands.

Would you play the lotto with these odds if it meant that you get a 1 in 4 chance of winning a very small jackpot, but you had to play Russian Roulette with three or four or five pulls of the trigger each time you played?

This become even worse if the “elusive breed characteristic” is not a simple recessive on a single allele.  What if “correct rear angulation” requires the alignment of several genes?  Inbreeding becomes less potent to line them up but it becomes no less effective in pairing up the recessive deleterious alleles.  Maybe only 1 in 16 or 1 in 32 puppies will have this nice ass, but the chance of any one of Tara’s recessive diseases showing up is still 1/8 for each one.

Inbreeding is using dynamite to do plastic surgery.

And did you catch that last sentence:

The plus is that the non appearance of genetic disease in the mature adults resulting from such a breeding are highly unlikely to be carriers of it, as well.

This is a horrible lie. Utter stupidity.  Just because the first guy to pull the trigger in Russian Roulette didn’t blow his brains out doesn’t mean there isn’t a bullet waiting in the chamber.  It’s a mathematical certainty that we expect to see 1 in 8 puppies affected with any single recessive disease carried by Tara.  If we dodge those odds and have no puppies that are doubled up, that scenario in no way changes the fact that we would expect to see 1 in 4 puppies being carriers for any single recessive disease carried by Tara.  Recombinant genetics doesn’t change the way it works to let inbreeding showple sleep better at night.

This statement is unethical and dangerous.  It is an insidious lie and Carol should be ashamed for spreading it.  This stupidity is the reason that inbred popular sires can be so devastating.  We assume that since they don’t have a given disease that they are highly unlikely to be a carrier as well, so heck, why not continue to inbreed on them?  This assumption has no basis in reality and gives a false sense of security, thus increasing the use of this dangerous behavior.  It is an Argument from Ignorance.  “I don’t see X, so Y can’t be there!”  Nonsense.  The absence of evidence is not evidence of absence, especially in this case.

Carol isn’t presenting a system of test breedings to ascertain a confidence level that her lines are free from defects–like a business will randomly test a few of its products to be sure that most of them are free from defects.  Instead she’s trying to co-opt that science in a half-assed way to say “look, I did this close breeding once and they didn’t all explode, so they MUST BE HEALTHY!”

Inbred Mistakes Series: (1) * (2) * (3) * (4) * (5)

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About Christopher

Christopher Landauer is a fifth generation Colorado native and second generation Border Collie enthusiast. Border Collies have been the Landauer family dogs since the 1960s and Christopher got his first one as a toddler. He began his own modest breeding program with the purchase of Dublin and Celeste in 2006 and currently shares his home with their children Mercury and Gemma as well. His interest in genetics began in AP Chemistry and AP Biology and was honed at Stanford University.