Inbred Mistakes V

By
Christopher
– Posted on November 16, 2010Posted in: Canine Health & Genetics, dogs, inbreeding mistakes

Shifting gears from an unrepentant pro-inbreeding propagandist back to fact-checking an otherwise excellent post, I’d like to take my editor’s pen to Christie Keith’s post at Pet Connection called It’s the DNA, stupid: Purebred dogs, closed studbooks, and genetic minefields.

The whole thing is worth a read, but the following passage is pure gold. Christie really hits on the unsung aspect of this entire debate:

The problem is something you can’t see, the genetic code of dogs who were never bred, who left no offspring: the genes we left behind.

Conformation traits that help dogs win in the show ring and give tabloid reporters and bloggers fodder for the outrage du jour are the product of selection on the part of breeders. Those observable problems that everyone is so eager to ridicule could conceivably be fixed by education and increased awareness. Lost genetic diversity causes far less fixable problems, like reduced litter sizes, reproductive failure, genetic disease, shorter life expectancies, lowered disease resistance, and greater rates of immune-mediated disease.

To put it another way, if your dogs can’t reproduce because their heads are too big and their pelvises are too narrow, that can be fixed if you pluck your own head out of your own hindquarters, but fixing a problem of inbreeding depression in an entire species is a task that daunts the most ardent conservationists and scientists.

This is the reason I’m doing these posts: not to defame the fancy, but to educate.  This isn’t something you were likely to have been taught in high school, certainly not in the depth required to make wise breeding decisions as a breeder or buying decisions as a dog owner.

The unbred dog will never win a ribbon or chase down a rabbit.  There will be no romantic novels written about the Border Collie who wasn’t inbred on Wiston Cap.  No photo-shoots for the dog whose face is symmetric but whose alleles are not.

Christie goes on to make another excellent point, that we are sacrificing the health and even future existence of our dogs to protect a word: “Breed.”  We aren’t even protecting a time honored definition of this word; the breeders who fashioned our many breeds out of the handful of historical landraces had no problems tampering with the recipe.

But enough with the plaudits, time for the criticism:

The “investigator” for “Pedigree Dogs Exposed” said in dire tones, “Being very inbred in and of itself has a catastrophic effect on the immune system,” but that’s not true. There’s no magical threshold of inbreeding that in and of itself causes health problems or impaired vigor in an individual dog. Unless the dog has inherited genes for a detrimental trait, there won’t be any negative effects.

This isn’t quite right.  We don’t need to put an exact number on an observation for an effect to be real.  As I have shown before, inbreeding and selection leads to a loss of information.  At the extreme, the same number of alleles tell a story that is half as long.  It is not true that deleterious genes need to be inherited.

Not every genetic effect has a name, let alone a disease associated with it.  We might call the Merle gene a disease, and we might call immune response depression a disease or a cluster of diseases, even if we don’t have a famous Doctor to name them after yet.

Let me run you through a hypothetical.  Let’s pretend that there is a single gene that controls blood flow to the uterus, and there are several different alleles for this gene: 8 units, 10 units, and 12 units of blood.  The optimal level which will produce the most puppies, is 10 units.

A dog might get two copies of the 10 unit allele and produce on average 10 units of blood feeding the uterus.  But the dog might be heterozygous with 12 and 8.  On average, this dog will also produce 10 units of blood, the optimal amount.  But a homozygous dog with 8 and 8 or 12 and 12 units will produce too little or too much blood flow, and consequently will give birth to fewer puppies.

Can we call this a disease? You might say that a puppy that is not born is about the same as a puppy that could have been born but died.  But this effect isn’t completely fatal, we’re still producing puppies even in the wost case scenario.

That’s a grey area, right?  What if the immune system works the same way?  What if we can’t put our finger on a fully fledged disease path but instead we have less efficiency in general?

We SEE this empirically with inbreeding.  But we are as of yet not fully aware of the exact mechanisms and possible disease paths.  So, just because we don’t have a named disease, we can not claim that there is no such effect.  We can’t even say that we need to inherit specific genes either, the effects could be partially epigenetic.  Until we know, we are foolish to close the door to what is possible.

I know “what if” questions are frustrating, but remember, we don’t even know all the rules we’re dealing with in biology, so we need to be careful to not fully dismiss what we DO observe experimentally just because it doesn’t yet fit into a nice box in a text book.

There are also breeds that have within them two or more pools of dogs that rarely mingle their genes, such as breeds with a strong field/show split like the Labrador Retriever, or breeds with a strong show/pet split like the Golden Retriever, or breeds with a performance/show split like the Greyhound.

If these populations of dogs within the same breed have genes that the others lack, then it’s possible to dip into those genetic pools and increase genetic diversity in your lines. You might not win in the show ring with those dogs, but you can do a lot to overcome inbreeding depression.

Unfortunately, mixing distinct gene pools within the same breed brings with it another set of problems, too. One, if you outcross among unrelated lines of the same breed, you risk eliminating the very pool of genetic diversity you were trying to preserve. Where will the dogs not descended from Ch. Popular Sire come from, if all his offspring got bred to those “unrelated” dogs in previous generations?

That last part is suspect.  While inbreeding fanatics smash the same genes into each other at an alarming rate, outcrossing is not an all or nothing proposition [nor need inbreeding be one either].  You don’t have to merge entire pools to achieve diversity.  For instance, in the Dalmatian Backcross project that Christie pointed to earlier in the essay, they bred to a pointer once, and once only and then worked the offspring back into the Dalmatian gene pool over 5 generations.  This produced dogs that were more than 99.9% Dalmatian.  We didn’t need to create a “Dalmointer” or whatever you’d call the F1 cross out of each Dalmatian line to see benefits.  Part of the problem is failing to differentiate between microgenetic and macrogenetic effects.  Whereas in a closed gene pool, you very well might reach a point that despite “outcrossing” you are still driving up COI (unavoidable inbreeding w/o leaving that gene pool), you will never reach a point where you are unintentionally out crossing despite trying to inbreed.

For example, the Golden Retriever is in no possible way put at threat because of the existence of the GoldenDoodle.  The Doodle is not contagious, and just because some Goldens were bred to Poodles, there’s nothing keeping the rest of the Golden pool from not breeding with a Poodle.  And, should the need arise to find an outcross for a Golden line, one might very well turn to a GoldenDoodle, but the results need not become widely bred back into Goldens right away.  A single smart outcross (or several) and then wise normal breedings back to Goldens (not even a need for intense inbreeding) could create several sires and dams with the desired new blood in the right places without sacrificing anything that would be quintessentially Golden Retriever.

It’s also worth noting that those quintessential aspects of our breeds are nearly universal, not only according to the process of genetic drift, but also the centuries of specific and ruthless selection.  While this process is the same one that has brought us problems, it most certainly can prove handy in our attempts to fix those problems.  It doesn’t take long at all after an outcross, even an extreme one, before the offspring begin to look and act like the root stock with few or no discernible variances.

We can have our cake and eat it too, because who wants to own cake and not eat it?  We’ve seen numerous examples of inbreeding into ruin and extinction, but really, can you think of a single example where someone out crossed into oblivion?  Did some Chihuahua breeder suddenly have a wolf pop out of her lines?  Have you ever seen an interracial marriage result in a Neanderthal or a Great Ape?  Recessives don’t disappear in outbreeding like information is lost in inbreeding and selection; they are at worst paired heterozygous and thus only “hidden” and not lost.

There are slippery slopes with inbreeding and selection because we are removing information and that information is lost.  There are no such slippery slopes with out breeding and inclusion. It is a constructive process, not a destructive one.  It is building with clay, not chipping away at marble.  Mistakes are never fatal, they can always be repaired.

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.