Population Genetics &  Hybrid Vitality

Genetic Diversity = Vitally Healthy Dogs!

What is population genetics?
HYBRID VIGOR & GENETIC DIVERSITY

Population genetics is a field of biology that studies the genetic composition of biological populations, and the changes in genetic composition that result from the operation of various factors, including natural selection.  A "crossbreed or hybrid" refers to an animal with parents of different breeds, varieties or populations. The process of breeding such an animal is practiced often with the intention of creating offspring that shares traits of each parental lineage, producing an animal with what is known as “hybrid vigor”. The practice of crossbreeding helps maintain the health and viability of the offspring, without incest breedings (aka -inbreeding & line-breeding).  For more info read our blog post about genetics.

Heterosis, also known as hybrid vigor or outbreeding enhancement, is the improved or increased function of any biological quality in a hybrid offspring. Heterosis in terms of breeding thus refers to the occurrence of a superior offspring from mixing the genetic contributions of its parents.

Based on the principal of "hybrid vigor," mixed-breed dogs are thought to live longer and generally be healthier than purebred dogs based on genetic diversity.
Specifically with dogs, a crossbreed refers to an animal that is a hybrid of more than one specific breed. Contrary to what some purebred enthusiasts will argue--the term HYBRID certainly applies to most dogs and should not be confused with a “mutt” or “mongrel”; these terms refer to dogs whose specific parentages are not known.

Historically, some of the oldest breeds were once hybrid dogs of two or more breeds. Today people purposefully and selectively cross-breed dogs to create specific new breeds of hybrid puppies. It’s no wonder that a growing population of dog lovers today prefer the genetically diverse background of the cross-breed over a purebred dog. In fact, recent studies have given rise to the belief that perhaps cross breeds/hybrids are healthier in the long run than their purebred relatives.  


Let's read on!

 

The Genetic Tide: Will it Leave Us High and Dry?
©1995 J. Jeffrey Bragg 
 

WE HEAR MORE AND MORE these days about genetic defects, with good reason. A year ago Time™ Magazine published a pre-Christmas exposé cover story on hereditary problems in purebred dogs. Now the Council of Europe urges EEC member states to adopt its "Multilateral Convention for the Protection of Pet Animals" banning the breeding of animals whose breed points handicap them, regulating breeders in an effort to halt the increase in inherited health problems. Many breeds we used to think of as hardy natural types -- even tough Arctic animals like Samoyeds, Siberian Huskies and Alaskan Malamutes -- are now routinely screened for four or five different genetically-related problems. These include deep-seated, serious disorders: central nervous system problems such as epilepsy, immune system malfunctions such as autoimmune thyroiditis. In addition to hip dysplasia, we now worry about osteochondritis, elbow and patella dysplasia, half a dozen distinct eye problems, and more.

At first it was thought that x-rays, screening and selection would ensure genetic health for our dogs. But thirty years of hip x-rays have not wiped out HD, although progress has been made in some breeds.
Screening and selection for one defect is just fine. But what do you do when suddenly five or six distinct problems must be screened for? Veterinary costs soar. You must select against so many traits that your breeding programme is turned upside-down. Especially if you fancy a serious working breed, as I do: you cannot manage a four- to six-way screening schedule and still select for working ability, breed type and conformation. In a small kennel on limited funds, breeding only two litters a year, it just isn't practical.
The books on dog-breeding hold no answers. They tell us how to use inbreeding, line-breeding and outcrossing, they teach us the basics of Mendelian genetics; these help to manage one or two traits at a time. But genes don't assort one trait at a time! Genes are linked in groups on chromosomes. While we were all using inbreeding and line-breeding to "fix" desirable traits of breed type and conformation, something else happened, and now we get a steady increase in unwanted traits that we call genetic defects.

The science of "population genetics" is old stuff to wildlife biologists, but few dog breeders in this country know much about it. Yet it could have told us about the problems that we would have by practising artificial selection, breeding from small founder groups with no new gene inflow for decades, using sustained incest breeding without the brutal tempering influence of natural selection.

Today, when most registered breeds are fifty to a hundred years old, bred within a closed Studbook the entire time, population geneticists tell us that we cannot continue these practices any longer if we want healthy canine companions. They say new genetic inflow is needed to counter random drift in small breed populations and to restore heterozygosity -- genetic diversity -- where it has been lost through inbreeding. They tell us that we are overusing popular sires and add that the German Shepherd Dog, despite millions of actual individuals worldwide, has an effective genetic population of from 400 to 600 animals only! Time-honoured breeding practices are now labelled "genetic genocide".
Breeds such as Salukis, Siberian Huskies, and Basenjis could easily restore hardiness and diversity by importing primitive stock from their countries of origin, but C.K.C.'s closed Studbook cannot accept such imports.

Perhaps the closed Studbook has outlived its usefulness. In the early days of purebred dogdom, it was a useful device to promote fixation of breed type. Now it has become a dead hand, dragging down the health of our beloved dogs.
The C.K.C., unlike most other Canadian livestock associations, makes no provision for grading-up, crossing, or new breed development. Its Studbook remains rigidly closed. Each C.K.C. breed is genetically isolated. No protocol exists for the acceptance of new foundation stock in C.K.C. breeds. The Club's procedures seem stuck in a nineteenth-century mould.
The upsurge in genetic problems -- and the media and government attention they attract -- make it obvious that radical change is needed. The question is, can it come in time? Or is our Club too inflexible to meet the challenge of placing real breed improvement above the demands of tradition and show-ring fashion? Is type more important than health? If we cannot breed healthy, hardy, happy dogs, there are those in our society who will question our right to breed at all.

-- This article was written just before the Seppala Siberian Sleddog became an evolving breed. It was published in "Dogs in Canada" magazine's February 1996 issue. Submitted by DIC to the Dog Writers Association of America annual competition, it won a Maxwell Medallion in the "Essays and Opinions" category for that year.

Liger

A Lion & Tiger Hybrid

Napoleon Dynamite wasn't kiddin'!

The Genetic Tide Continues to Swell:
Will DNA marker research stop the flood?
 ©1998 J. Jeffrey Bragg


The tide of concern about genetic health continues to swell within the purebred dog fancy, driven on by scrutiny from without. The threat of punitive legislation, already a reality in Europe, is widespread in the USA and the contagion seems certain to reach Canada as well. Conventional screening methods appear to be a proven failure as far as curing genetic disease (rather than simply reducing it somewhat). As veterinarian breeder Ms. Chidiac-Storimans once wrote in Dogs in Canada, "obviously, breeding clear to clear does not work." Yet great optimism is expressed in canine journals despite the seeming crisis proportions of genetic disease.

DNA marker research now holds the limelight. The US $750,000 canine genome project at the University of Michigan, reported in the press in 1990 as expected to identify DNA marker sequences for over 400 canine genetic diseases, has actually established 625 markers and as a "demonstration project" was able to link one marker to a specific genetic disorder, copper toxicosis in Bedlington terriers. This and several other DNA tests for breed-specific disorders are now marketed by VetGen in Ann Arbor MI, where the University is also located. The Scottish Terrier Club of America recently paid US$50,000 to establish a DNA marker for canine von Willebrand's disease in their breed; other breed clubs are reportedly queueing up to pay similar sums for similar purposes. Obviously there is money to be made in canine genetic diseases, though perhaps not by dog breeders.

Even if every breed club had that kind of money to spend on marker development, and every breeder could afford $50 to $135 per test for all his dogs, there would remain plenty of room for doubt concerning whether the strategy of DNA marker tests followed by radical selection and culling would solve the problem of genetic disease.  Gene pools of purebred dog breeds, already stripped and impoverished of genetic diversity by twenty or thirty generations of inbreeding and selection, may not withstand a massive wave of radical selection followed by yet more inbreeding. What happens when all or most individuals in a breed turn out to be "carriers" of the same defect? Breed gene pools represent only a fraction of the total canine species genome. Genetic diversity in purebreds is limited from the outset, by selection inherent in breed development and by the sometimes distressingly small numbers of founder animals when breed registries are first established. A gene pool is like a bank account - you cannot make withdrawals forever and never make a deposit. Yet the closed studbook system prohibits making more than one deposit! The fetish of "breed purity" demands that after the founder registrations the stud book must remain forever closed to new genetic input. When examined closely this concept of strict breed purity must be regarded as a racist ideal, similar in nature to the "scientific racism" promulgated by Hitler's Nazi party. Why do we denounce racism and eugenics on the human level, only to turn about and defend the selfsame ideals as the only decent norm for breeding dogs?

Any description or defense of a project involving breeding across existing breed lines for practical purposes, such as the Wirehaired Pointing Griffon Club of America project, is met with aggressive rebuke. If every effort to restore genetic health, hardiness, or working ability through outcross breeding is to be condemned as a betrayal of the "purity of the breed," then the entire purebred dog concept may be doomed to failure through inbreeding depression, the general loss of vitality and viability. Those who are quick to stigmatise serious outcross programmes as "Foufons" and "crossbreds" betray their utter ignorance of population genetics, yet that ignorance still meets with general approbation. Too bad, because at this point, the application of population genetics principles may be the sole strategy that can possibly pull the purebred dog fancy out of its genetic dilemma.

Genetic diversity is held to be essential to maintain species soundness and environmental fitness, but genetic diversity is what most purebreds seriously lack. Responsible scientific opinion now connects this lack of diversity with the canine genetic crisis. However much the racist mind may condemn the idea, there is but one way to restore lost genetic diversity in a population, and that is by new gene inflow - in other words, by outcross breeding. When will the purebred dog fancy awake from its dream of purified bloodstreams and allow the new gene inflow necessary to restore genetic health to our dogs?

(This article by J. Jeffrey Bragg was a followup to the award-winning DOGS IN CANADA article "The Genetic Tide: Will it Leave us High and Dry?")

 

An explanation from Neils C. Pederson at UC Davis, excerpted from a current PCA grant proposal below:

All autoimmune diseases recognized to date in dogs and humans have one thing in common—they all are associated with genes that regulate the immune response. These genes are gathered in a distinct region on the dog chromosome 12. An identical region, albeit located on different chromosomes, exists in all species of mammals and birds and is known as the major Histocompatibility Complex (MHC). The MHC of the dog has been designated the “dog leukocyte antigen’ (DLA) complex. The MHC (DLA) is divided into four regions, containing Class I, II, III, and IV genes.

A strong association between autoimmune disorders and the DLA class II genes has been shown for a number of disorders, including Pug Dog Encephalitis(6), a Vogt-Koyangi-Harada (VKH) like disease in Akitas (7), autoimmune hemolytic anemia, immune arthritis and hypothyroiditis in several breeds (8-10), type I diabetes mellitus in Samoyeds, Cairn and Tibetan Terriers (11), anal furunculosis in German Shepherd Dogs, and a systemic lupus erythematosus-related complex in Nova Scotia Tollers (13). This supports the hypothesis of Svejgaard (14) that many autoimmune disorders of humans, and now dogs, may be MHC- associated.

Autoimmune disorders, affecting a wide range of organs and tissues, are becoming increasingly common in purebred dogs. The main reason for this is a decrease in genetic diversity within the various genes of the DLA complex. This loss of diversity is particularly noticeable with the DLA class II genes, DLA-DRB1, DLA-DQB1, and DLA-DQB1. There are currently 143 known alleles for DRB1, 26 for DQA1, and 66 for DRB1.(April 2010) . In all dogs, these various alleles are linked in various three-gene combinations called haplotypes. Over 143 such haplotypes have been found in the DLA across all dogs. (2010) However, most purebreds have only a handful of alleles at each of these three gene loci, and have as few as 4 to 8 haplotypes in the entire breed (18, 19).

The main function of the MHC (DLA in dogs) is what is called self/non-self recognition. The immune system must be able to identify every foreign protein that invades the body, whether it is on a bacteria, virus, fungi parasite, etc, as being “non-self”. Conversely, the body must be able to recognize every protein that is part of itself and not react immunologically to it. As genetic variability is lost in the DLA, the ability to differentiate between what is self and what is non-self becomes more and more tenuous.
 
When discernment of what is self from non-self becomes extremely difficult, the body will mount an immune response to its own proteins. The first self proteins that are recognized as foreign are most often the product of glands (thyroid, sebaceous glands, perianal glands, adrenal glands, tear glands, parathyroid glands) and the proteins on the surface of blood cells (white cells, platelets, red cells). This is probably because the proteins on these types of cells more closely resemble the proteins on invading (foreign) pathogenic organisms.

The Original Habibi Bear
Genetically Diverse - Hybrid Vigor - Healthy

Parent Breed Infusion

The Habibi Bear's ancestry is an infusion of  diverse, healthy  breeds.  Each breed was selected for the unique traits they bring to the gene pool.  Each generation was carefully combined, to ensure optimal genetic diversity without line-breeding or in-breeding. Not a simple cross breed, this breed boasts 5 breeds in the background! This is hybrid vigor on steroids.  We have maintained the level of genetic diversity (hybrid vigor) without doubling up on same breed lines.  The Habibi was bred to be the perfect hypoallergenic companion animal that excels as a service, ESA, facility or therapy dog.

Our hybrid dogs, The Habibi Bear, are a healthy breed.  We attribute this to the wide gene pool.  No known genetic issues have been detected through our testing on our parent dogs in our breeding program.  All Parents have been Health-tested & DNA tested through Paw Print Genetics. We only breed healthy dogs.

Genetic Testing Facts You Should Know

Our adult dogs are carefully paired for optimal health and vitality in their offspring. We strive to produce healthy hybrid puppies, and this is why we offer a 5 Year Guarantee on all of our dogs.  In safeguarding the health of our Habibi Bears, we need all the information available to help us with the development of our breed. Testing and careful breeding work hand in hand.

Tests are tools to be used by breeders for making sound decisions. They certainly do not ensure that a puppy will be healthy, or guarantee you will receive a replacement if your dog develops a genetic problem. Only an extensive health guarantee does! That is why the background knowledge of the breed and the dogs behind the parents is important.

Health Issues with purebreeds & inbreeding

Hybrids

There are significant differences between a crossbreed and an inbred dog. An inbred dog is one whose parents were closely related to one another; this often results in brain damage, health problems and deficiencies in physical development. While inbreeding will occasionally happen by accident, a responsible dog owner will avoid this mishap at all costs. We avoid these issues related to inbreeding all together – by keeping a close eye on our lines, staying in touch with families that have adopted a puppy from us and working closely with our veterinarian.   

Inbreeding

Purebred dogs often have many congenital problems from inbreeding; the most common being hip displacement. Breeding dogs prone to parallel health troubles significantly amplifies the risk of health problems in the litter. When two dogs of varying breeds and health issues mate, the odds of serious health-related harms are decreased. Since hybrid dogs come from a wider gene pool they tend to have fewer problems. A crossbreed is definitely not a lesser dog than a purebred. There are a lot of positive benefits to adopting hybrid puppies as opposed to a purebred, and many prospective dog owners choose to adopt the hybrids for their qualities.


You may have heard that purebred dogs are "inbred" and therefore plagued with inherited health problems, as well as nervous, high-strung dispositions. To some extent, this is true of poorly bred purebreds. There are many incredible purebred breeders out there and we love and adore our purebred dogs, so this is in no way a judgment call purebred vs hybrid dogs.  For our purposes, we chose to develop our own breed, but have been involved in dog fancy prior. The reality is that all living things are prone to inherited problems, and dogs are no exception. Purebred dogs do inherit problems, as can any dog that is not bred using responsible breeding choices.

All of the purebred dog breeds in existence today came about in one of two ways.  Breeds developed out of rough groupings of animals from a particular geographic region loosely selected and interbred for a specific function. For example, poodles fall into this category. As do the "rough" terriers of the British Isles who were divided into several dozen separate breeds based on physical characteristics, color and locale. When showing and breeding dogs became fashionable during the Victorian era, many of these landraces were divided into multiple breeds. In short order, stud books were established and standards were written for each. Additional crosses were initially made as needed to improve performance or to correct structural defects. Once breed type was established, stud books were closed and no further new "blood" was allowed.

The second method of creating new breeds in the Victorian era came about through hybridization, or the deliberate crossing of two or more already established breeds. Now, many show breeders insist hybrid puppies are the offspring of two different species and therefore the statement "there are no hybrid dogs" is flat-out incorrect.

The Golden Retriever, the Doberman Pinscher, the Boston Terrier, the Bedlington Terrier and the Wirehaired Pointing Griffon are all examples of breeds whose creation for a particular purpose through hybridization are well-documented and each attributable to a single breeder!

Within a few generations these "new breeds" were accepted along with the landrace breeds into the newly established all breed registries, notably the Kennel Club in England and the American Kennel Club in the US.

Cross Bred or Hybrid Dogs

Most breeders of Hybrid puppies and the informed pet-owning public would disagree. Comparing of Hybrids to Mutts  is like comparing apples to oranges.  As we have learned, science suggests a much different situation.  One survey shows that over 50% of Puggle owners had previously bred or owned purebred dogs at one time or another, and that it was due to struggling with health issues that they investigated other options for dog breeding.

Breeders and prospective families alike choose hybrids because they want more predictability in size, temperament and coat than they would have with a mixed-breed of unknown parentage, without the heartbreaking and often expensive health issue that they have experienced with their previous purebred dogs.

Can hybrids deliver on this promise?

Within certain parameters, there's absolutely no reason to assume that they can't. So how much trouble are purebred dogs, from a "lack of diversity in the genes that control immune function" standpoint? Apparently, more than was originally believed. Although most breeds have 4-7 DLA haplotypes (out of a possible 11,000,000 possible combinations), research has shown that in most breeds tested, over 70% of the dogs within each breed share only 2 haplogroups, and close to 50% are homozygous.

"The most logical and painless way out of this dilemma is to simply press upon the advantages of hybridization that created many of these breeds in the first place. Refusal to do so because of some antiquated and scientifically discredited notion of "genetic purity" is, blatantly ignorant."  

Science tells us the TRUTH!

All dogs have something that makes them special to their owners. Whether it's the knowledge that Champ has the strength and vigor of ten dogs put together, or the fact that you know  Lady could whoop the fur off the Poodle next door in the show ring, everyone has something that attaches them to their pet emotionally. They're all there for us at the end of the day, ears perked and tails wagging. In the end, hybrid dogs versus purebred dogs is just another silly contest. You don't have to be blood (pure or otherwise) to be family!

An article written by a Geneticist on the subject, which supports our position on genetic diversity and responsible breeding practices. 
Here’s what Hekman, the dog geneticist, wishes dog lovers knew about genetics:

What do dog lovers seem to get wrong about dog genetics? “Thinking that genetics are destiny — that if a problem is ‘genetic,’ it can't be changed. Sometimes that's true, but very rarely in the case of behavior problems. A dog's personality is inextricably made up both of genetics and experience, and if you're seeing problem behaviors, it's always worth exploring what it might take to fix them. (On the other hand, if you're trying to get your retriever to be less interested in balls, this is likely to be an uphill battle.)”

What do you wish purebred dog owners knew about dog genetics? “Inbreeding is real and is a serious problem in many, if not most, pure breeds.”

Hekman has previously weighed in on this topic. In the post ‘How to Make the World Better for Dogs’ at Companion Animal Psychology, Hekman describes a number of well-known challenges that purebred dogs face. Here’s Hekman: “We can make the world better for dogs by making dogs who fit into the world better. I would love to see dog owners draw a line in the sand and insist on dogs with muzzles long enough to let them breathe normally, or dogs who are not born with a 60% chance of developing cancer at some point in their lives due to their breed, or dogs whose heads are too big for them to be born without a C-section. I'd love to see more breeders taking matters into their own hands and starting to experiment with how we breed dogs instead of continuing to use dogs from within breeds lacking in genetic diversity. I'd love to see more breed clubs supporting outcrossing projects to bring an influx of genetic diversity and healthy alleles into their breed. I'd love more dog lovers to become aware of the problems with how we breed dogs — how even the most responsible breeders breed dogs! This year, it is time for change.”

What do you wish mixed-breed dog owners knew about dog genetics? “Finding out the breeds that make up your mixed breed dog is unlikely to be helpful in predicting your dog's behavior or future health problems. It's just fun!”ed in mutts. Based on earlier studies, this might be more difficult than you’d think. Give it a try!

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