Inbreeding is like screwing yourself over and over again.
And it produces about the same results. It starts alone, in the dark, with good intentions but you’re settling for self-soothing because you couldn’t get what you wanted from someone, anyone, else. And in the end you end up a shell of a being only half as fulfilled as you could have been.
It feels good at that moment because it is instant gratification. You don’t have to worry about being “approved” by the other party, no “stud fees” required. Results in minutes. You don’t have to study, seduce, or even try to understand the other players in the game. Just know your own “lines,” no scary new experiences required.
But it’s lazy and it makes you complacent. Why put the effort in finding satisfaction elsewhere when that might require effort, time, money and risk rejection and disappointment?
Sure, you might venture out from the basement once in a blue moon and pay for some “strange” but it’s so much easier if you lower your standards and keep full control; after all, who knows your lines like you do? Love yourself! If you don’t mingle naughty bits you’ll never get a new disease!
While it’s more of a male thing, females get involved too, although rarely with the obsessiveness and fervor of the male strain. Rampant mocking and endless jokes about it haven’t done much to make anyone stop doing it.
Although we don’t enjoy admitting it, almost everyone did it in their adolescence to prepare for the bigger challenge of swapping genes with another being in the dating pool, and sure, it still has its place in a healthy and circumspect sex life, but if you do it too much you probably will go blind or grow hair in places you don’t want or make it fall out of places you do.
In fact, self pollination (“selfing”) is the most extreme form of inbreeding, and it’s thus the most powerful tool to accomplish the goal of any form of inbreeding or line-breeding: homozygosity. Homozygosity is Greek for “one and the same yoke” and is the state of having two identical copies (alleles) of a given gene.
The reason breeders select for homozygosity is because having two identical copies of a specific gene means that the animal will be guaranteed to display the trait associated with that gene and is guaranteed to pass that allele along to its offspring. If that gene is dominant, it will again be guaranteed to be expressed in the offspring, if it is recessive, being homozygous in both parents will guarantee expression in the offspring.
It’s WYSIWYG for selective breeding. Breeders call this quality “prepotency.”
A stud animal of any species is judged on his pre-potency, which means that not only must he exhibit the best phonetic traits himself, but he should also demonstrate his ability to pass along these traits to his progeny over a diverse female population.
The greater theory of Prepotency is bunk: that superman sires should be able to overcome any problems in the dam, ideally the female being but a vessel to produce perfect copies of the sire. What isn’t bunk is the very real effect of rising homozygosity: the more homozygous the parent, the less variation in genes passed along to the offspring.
Likewise, line breeding and inbreeding are really no different in their effect or results, good and bad, they only differ in what percent of alleles are likely to become matched each attempt.
There is no way to double up on desired genes and not on undesired genes, and the truth is that people inbreed for the purpose of doubling up on a very small number of genes while they have no interest in the millions of other genes becoming homozygous. What is good for locking in a harmless coat color gene could be disastrous for all of the deleterious recessive genes that are also getting doubled down on unintentionally.
And the ratio of unintended doubles vs. intended doubles in any given breeding is easily many-thousands to 1. The canine genome has ~3 billion base pairs and the most focused on genes like coat color and structure make up a small percent. Harmful mutations start out rare, but with odds like these, it’s not surprising that they rear their ugly head in every breed.
Inbreeding is like burning down the forest to fell one tree.
To demonstrate how dramatically inbreeding can transform a heterozygous (maximum genetic diversity) individual into a homozygous one, I’ve run a simulation on self-pollination. The act of “selfing” is twice as potent a force as a father x daughter mating or a sibling x sibling mating in its ability to pair genes: selfing is expected to double up 50% of the alleles in any generation, whereas a father x daughter mating is expected to double up 25% of the alleles. Both are potent and dangerous.
In the upper left we have a representation of a fully heterozygous individual. All of its genes are paired Aa, two different alleles at every location. It’s a universal carrier. Each different row can represent a single gene or a group of genes, and to easily track how these alleles can jump around from left and right and recombine, I’ve painted all the alleles on the right blue, all the alleles on the left red.
Although the intervening steps look more chaotic, they actually represent a loss of information. Remember that matching colors up and down the chromosome isn’t what matters, it’s matching the colors in the same row left and right. The chart below shows the alleles that are lost forever by continuing to breed on this line at each stage.
As we move to the right, the resulting chromosomes are the product of “breeding” the previous chromosome with itself. The results were randomly generated. Thus we are both inbreeding and selecting as we move right just as we would in a breeding program.
This random progression is a good representation of the average scenario of continued selfing. The chart on the left shows what the expected degree of doubling up would be each generation. You can see how fast this converges on 99%, so even if we lucked out in the first generation and got only 15% or 25% doubling, successive inbreeding would still converge quickly to the extreme.
Inbreeding alone doesn’t cause loss, it doesn’t even change the frequency of alleles in the offspring taken as a group. It simply changes the ratio of those alleles from being mostly mixed Aa into mostly paired, AA and aa. What causes the loss of information is that breeders don’t inbreed blindly and randomly select offspring. They select very few offspring each generation to breed, thus large amounts of genes are lost. We inbreed and then select so few offspring to continue the line. Since these offspring carry less individual information, the loss of information from culling is magnified greatly compared to the same selection process working on heterozygous offspring.
The logical and definitive result of continued inbreeding is to create what is essentially a half-being. And these two halves don’t make a proper whole. Even with a less extreme form of inbreeding, one available to dog breeders like father to daughter (25%) or sibling to sibling (25%), the ability to quickly drive up the Coefficient of Inbreeding (the percent of genes that are expected to be homozygous resulting from doubling a single allele from the same ancestor) abbreviated COI or F is still dramatic.
COI/F is both the probability that two alleles in an individual are identical by descent and also the proportional decrease in heterozygosity under inbreeding.
What’s disconcerting is that you don’t have to get to extreme levels of inbreeding/homozygosity before the offspring are not viable. A Border Collie breeder tried to recreate Wiston Cap by inbreeding very highly on him and his offspring, reaching a COR level of over 80% and a COI of over 60%. No sustained offspring.
That’s not a surprise as we see inbreeding depression on offspring from the plant kingdom all the way up the food chain. Inbreeding tries to take care of itself. But in a dog culture where most breeders covet their copy of “Puppy Intensive Care” where you can triage a puppy that nature would cull long enough to drop a fortune on it until it’s breeding age, we not only don’t allow nature to correct itself, we push as hard as we can using the most devastating and blunt tool we have available to emphasize the extreme and leave fallow the middle ground.
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Nice imagery.
I’ve heard the popular sire effect is a real issue for Vizslas. I’ve always liked that breed, but one I know well just died of cancer at the age of six.
SIX!!
Doesn’t bode well.
Ruth Crisler recently posted..Bed Bugs Beware
A link to this should be posted on every breed club and registry website.
Five years ago I was looking for a herding breed dog. After being turned down as a poor prospect by four different “rescue” groups, I started looking at breeders. Having owned a half dozen or so Aussies, and having liked most of them, I checked out some local Aussie breeders. The first one I found was advertising the wonders of a litter out of a pair of highly inbred littermates.
I ended up with a Kelpie I picked up from a goat farm.
Janeen recently posted..Beautiful and yet…
Excellent post, well summed up also for those who do not master genetics
Jonzie recently posted..When youll be finished
Awesome post, I am not a master of genetics by a long shot but now more than ever I understand.
Thank you!
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http://www.retrievertraining.net/forums/showthread.php?t=75425
Inbreeding can be a useful tool in some breeds. If you do this you better be prepared to cull up to a year old or more. It may take that long before the dog shows it doesn’t have what it takes in brains to do the work the breed was developed to do.
Inbreeding has certainly been billed as a useful tool, but what are the results? Not very good. If your breed is so small that you have to look to closely related dogs to find what you want, then you’re only further drying up a small gene pool. If you have a large breed, you should have plenty of opportunities to find good mates that aren’t closely related but still carry the type you want. If you can’t find that, I think you should re-investigate your priorities.
Thank-you for this post. I often find the inbreeding debate gets highly emotional, and this article was excellent in being very factual. Thank-you for compiling it.
The examples you have used are a bit extreme – breeding father to daughter/grand daughter/great grand daughter for 25 generations would be a very strange occurrence, and I would run a mile from any puppies produced from such a breeder.
Line breeding is useful for solidifying traits. For example, if you had a free whelping pug bitch, you’d very much want to capitalise on her free whelping genes, and may choose to line/in breed in order to try to replicate this trait in her progeny. However, very rarely is line breeding done for these reasons: Most of the time breeders want to get nice heads, nice coats, which are less significant to the well-being of the dog than their whelping ability.
Your infant mortality re: COI is very interesting. Thanks for posting. What study does it come from?
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Thanks Tegan.
Yes, the chart of father x daughter is really an upper limit calculation. While few breeders could hope to maintain that level of inbreeding, sadly the effect on homozygosity is not that far off under actual scenarios.
First, many breeds are highly homozygous to start with, in the area of 40-60% in non-inbred dogs. The chart starts at 0% and assumes you begin with a fully “outcrossed” i.e. heterozygous dog.
Also, notice how fast the chart approaches 90%. You really don’t need 15 or 20 generations to have a huge loss of genetic diversity.
The charts are from this powerpoint, hopefully you can track down the source material:
http://courses.washington.edu/vseminar/Esc458-7/LECT7.PPT
Thanks for the link to the powerpoint. I look forward to reading it in more detail at a later date. 🙂
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I don’t know much about any of this . But my daughter breeds Yorkshires. She did not do it on purpose but they got out of there enclosures and son breed with mom. My daughter kept a girl and grandson kept a boy. My daughters Yorkie will attack any other dog and she is going to kill she goes for the throat and wont let go .She has hurt my tiny Maltese and min-pin a couple of times. She is staying with me right now the dog cries non stop or barks my daughter says she is jealous but I think not. Is this normal??I am stresses to max .And I mean every chance she gets she runs straight for first dog she can get her mouth on it is almost impossible to get her to turn loose.
Connie –
Yorkshires are still terriers and they were at one point bred to kill vermin. And they are also known for dog aggression. This is a problem that you might be able to mitigate with training, but there is also probably a very strong biological component and the close inbreeding does not help that at all. If you can not find a means to make this dog happy in life, putting it down might be the most humane choice for you, your other dogs, and the dog in question.
Bleeding heart types who want to save every single dog ever will “manage” a dog with severe dog-aggression. This is also called “crate and rotate” and it operates something like a prison. You keep the problem dog in its crate and when you want to allow it out, you put all your other dogs in a different crate and so they are allowed access to outside and the house, etc. but not at the same time. It turns you into a prison warden that is constantly trying to keep dogs that will otherwise injure or kill each other apart. It’s not a fulfilling relationship with the dogs.
So consult a trainer. Get help. And assess if that has any change in behavior. If not, consider if you really want to keep risking your other dogs’ and your own safety to keep this inbred dog alive and suffering itself. I don’t believe any dog enjoys attacking other dogs for fun, they attack because they are either afraid or mentally unstable. They don’t attack because they are stable and just think it’s fun. It’s a mental disorder and the dog in question is likely suffering, not to mention the suffering of your other dogs who are now not safe in their own home.