Purebred Dog Breeds into the Twenty-First Century: Achieving Genetic Health for Our Dogs



What is a Canine Breed?

What is a breed? To put the question more precisely, what are the necessary conditions that enable us to say with conviction, "this group of animals constitutes a distinct breed?"

In the cynological world, three separate approaches combine to constitute canine breeds. Dogs are distinguished first by ancestry, all of the individuals descending from a particular founder group (and only from that group) being designated as a breed. Next they are distinguished by purpose or utility, some breeds existing for the purpose of hunting particular kinds of game,others for the performance of particular tasks in cooperation with their human masters, while yet others owe their existence simply to humankind's desire for animal companionship. Finally dogs are distinguished by typology, breed standards (whether written or unwritten) being used to describe and to recognize dogs of specific size, physical build, general appearance, shape of head, style of ears and tail, etc., which are said to be of the same breed owing to their similarity in the foregoing respects.

The preceding statements are both obvious and known to all breeders and fanciers of the canine species. Nevertheless a correct and full understanding of these simple truisms is vital to the proper functioning of the entire canine fancy and to the health and well being of the animals which are the object of that fancy. It is my purpose in this brief to elucidate the interrelationship of the above three approaches, to demonstrate how distortions and misunderstandings of that interrelationship now threaten the health of all of our dogs and the very existence of the various canine breeds, and to propose reforms which will restore both balanced breed identity and genetic health to CKC breeds.

In order for canine breeds to fulfill their destinies effectively, the three distinct axes along which breeds are distinguished must have equal importance and consideration, otherwise serious problems arise. Breeds cannot be distinguished by ancestry alone, by purpose alone, or by typology alone. Unless these three vectors of breed identity interrelate fully and cooperatively, the fullness of that identity is missing or marred. Unfortunately, this full and cooperative interrelationship is a rarity in our contemporary dog world. The criteria of ancestry are applied rigidly and mechanically; the criteria of purpose and utility are subordinated or not considered at all; the criteria of typology are applied in a highly exaggerated, obsessive fashion. The interaction of the three approaches is seldom considered and almost never is a sustained effort made at the integration of the three.

The Origins of Dog Breeds

Canine breeds come into existence in many different ways and their beginnings are very often shrouded in obscurity. Let it not be thought that the three or four hundred-odd dog breeds now extant are the only ones possible, or that there cannot be any more truly new breeds. Such is the genetic plasticity of the dog that there is no end to the possible unique variations of which the species is capable. New breeds are born and old breeds die periodically. The genetic transformation of the dog goes on ceaselessly, and for that reason it is impossible that any breed should remain frozen, with all its characteristics fixed and unchanging, for any appreciable length of time. It must be realized that canine breeds are manmade, created by artificial election out of the endless diversity of the canine gene pool. Breeds must not be confused with species or even subspecies, which occur naturally under the influence of natural selection; dog breeds are only unstable manmade varieties which would not survive unchanged in the natural world without human management.

An important characteristic of breeds is that they are created by breeders -- not by registries or protective organizations such as The Canadian Kennel Club. The origin and course of a canine breed is in the hands of its breeders, first, last and always. It is the business of cynological associations to facilitate and support the work of dog breeders and not vice versa. The purposes of the Animal Pedigree Act, under which CKC is incorporated, are the promotion of breed improvement and the protection of those who breed and purchase animals; such is the mandate of the Act and therefore of the Club [Animal Pedigree Act, §3(a,b)]. All else is secondary.

Ordinarily a breed has already existed for an appreciable length of time before it reaches the point of becoming a recognized breed served by a registry. Nonetheless, the event of its "recognition" by a registry such as CKC is always a crucial one in the history of a breed. As things now stand, breed recognition is far more crucial (and ultimately damaging to the welfare of the animals) than it need be or ought to be, but more of that anon. First let us examine what is needed to start a new and unique canine breed.

Four essential characteristics usually distinguish the origin in the genetic sense of a new breed (as opposed to the discovery, popularization and "recognition" of, for example, an autochthonous breed which may have existed in a particular region for a long time without connection to formal cynological structures). The first and most crucial characteristic is the founder event in which a finite number of individual canines is chosen to contribute genetic material to found a new and unique canine population. They may all be quite similar, or they may be widely divergent one from another (as when Bulldog and Mastiff specimens were used to create the Bullmastiff breed). What matters is that a finite and sometimes quite small number of individuals are selected from the existing canine population and set apart so that their genetic material alone forms the gene pool for the new breed. That is in fact the next characteristic: isolation. If the founder group continues to exchange genetic material at random with the general canine population, a new breed will not result. Without genetic isolation of the new founder group, the differentiation that creates a new breed cannot take place. The logical consequence of this isolation is the next characteristic: inbreeding. If the founder group is of small or moderate size, such inbreeding cannot help but occur. Even if the founder group should be quite large, ordinarily those who guide the breeding which creates the new breed will find it necessary at some stage to employ a strong degree of incest breeding or inbreeding, to facilitate the weeding-out of undesired characteristics and the fixation of desired traits. Particularly if individuals of widely divergent type and physique are involved, inbreeding will be required to set up a stable genome in which random variability is kept within limits defined by the breeders. The final essential factor is artificial selection, since inbreeding alone will not serve to fix type characteristics and to eliminate unwanted traits. The breeders must select among the individuals produced in early generations so that only hose displaying the desired characteristics are allowed to produce subsequent generations. Without the four factors of the founder event, isolation, inbreeding and artificial selection, new breeds ordinarily do not come into existence. These four tools are used to define a new genome which, hopefully, contains only the traits desired by the creators of the new breed and is able to reproduce itself, with its distinguishing characteristics, to a fair degree of stability and consistency.

The Healthy Continuation of Breeds

Purebred dogdom is even now in serious trouble through a general failure to distinguish between what is necessary to establish a breed and what is desirable to continue that breed in perpetuity. Most registered breeds are less than a century old as registered breeds; many are but fifty or sixty years old. Yet nearly all breeds now show levels of expression of genetic defects that must be considered unacceptable. Over 500 distinct genetic defects have been cataloged in various breeds of purebred dogs and more continue to come to light regularly. Some of these have reached very high levels of incidence, creating problems for breeders and dog owners, threatening the health of entire breed populations. What is worse, in many instances organized control programs seem relatively ineffective. Although such programs successfully identify affected animals, in some cases individuals with several generations of "clear" ancestry stubbornly continue to produce affected stock. Let us try to examine what has gone wrong and what must be done to correct the situation.

First of all it must be recognized that practices which were essential for the differentiation and establishment of a new breed may not necessarily be desirable for its continuation over time and may in fact be prejudicial to a breeds continued existence over the long term.

Let us take isolation, for example. Without genetic isolation, it would not be possible to control the genome of a new breed still few in number. It takes time and careful breeding to fix a new combination of characteristics; while that is being done, the regular addition of new genetic material would generally be counterproductive. Yet in the long term, if genetic isolation is maintained, it will necessarily lead to degeneration through genetic drift. Similarly inbreeding, if it continues to be practiced after the need for it is past, will lead to a steadily increasing state of homozygosity which may well destroy the genetic health of the new breed. Even artificial selection, if carried on too strongly for too long, can combine with isolation and inbreeding to reduce drastically the effective breeding population, thus eroding the genetic health of the breed.

The Fallacy of Breed Purity

The present structure of The Canadian Kennel Clubs studbook registry (and others like it) embodies a fallacy which is directly responsible for the current genetic crisis in purebred dogs: the fallacy of breed purity. The ideal of the purified lineage is seen as an end in itself; accordingly, the studbook has been structured to reflect and to enforce that ideal rigidly and absolutely. This insistence on absolute breed purity arises from nineteenth-century notions of the "superior strain" which were supposedly exemplified by human aristocracies and thoroughbred horses; this same ideal, pushed to an illogical conclusion on the human plane, resulted in the now discredited "scientific racism" of the Nazis, who tried through selective human matings to breed an Aryan superman. The idea of the superior strain was that by "breeding the best to the best," employing sustained inbreeding and selection for "superior" qualities, one would develop a bloodline superior in every way to the unrefined, base stock which was the best that nature could produce. Naturally the purified line must then be preserved from dilution and debasement by base-born stock. There is no support for this kind of racism in the findings of modern genetics -- in fact, quite the opposite: population groups that are numerically limited and closed to new genetic inflow are now thought practically certain to be genetically inferior. Certainly towards the close of the nineteenth century it became embarrassingly obvious that the human aristocracies of Europe were degenerating rapidly under their own version of the "closed studbook."

The ideal of breed purity as applied to purebred dogs has resulted at the end of the twentieth century in a subculture that holds "purebred" registered animal stock to be qualitatively superior to crossbred or "mongrel" stock. (The word "mongrel" is in fact part of the vocabulary of racism, being applied equally to canine stock of no recognizable breed, to animal crossbreeds and to persons of mixed race!) In this subculture -- presided over in Canada by the CKC -- it is thought to be of paramount importance that purebred stock be maintained unsullied by any genetic influence external to the supposedly superior strains that are produced by registered breeding in a closed studbook from a small group of foundation stock. New members of the CKC are required to subscribe to "Conditions of Membership" whereby they promise to have nothing to do with "dogs which are not purebred" (with the exception of family pets and boarders), "purebred" being specifically defined as referring only to dogs "registered individually or eligible for registration in records of the CKC." Litters which are made the subject of complaints that they may not be purebred are investigated and in many cases ceremoniously withdrawn from the registry by resolution of the Clubs Board of Directors. Whether you like the word or not, this is effectively a special variety of racism in concept and in practice.

Not all dog breeders are in agreement with the proposition that breed purity is more important than anything else, particularly when they are confronted with the problem of breeding dogs to demanding performance standards. Mostly such dissenters are obliged to carry on their breeding without the benefit of centralized pedigree record keeping and official certificates of registration -- for example, those who breed "Alaskan huskies", the high-performance racing sled-dogs that dominate both short and long distance dogsled racing, keep pedigree records and maintain sophisticated breeding programs, but only as individual breeders. Yet sometimes even participants in established purebred registries engage in a subtle kind of rebellion, quietly breeding according to their own judgment in defiance of formal restrictions. Thus the Racing Greyhound Club of Australia, when it recently subjected a broad sample of stock from its registry to DNA testing, is rumored to have discovered that many pedigrees failed to match DNA ancestry findings and that considerable interbreed crossing had apparently occurred. Similarly most Siberian Husky fanciers are aware that some CKC bloodlines may have received surreptitious infusions of genetic material from non-purebreds or from other breeds. In some circles one even gets the distinct impression that "its OK to crossbreed occasionally if you have a good reason for doing it and you manage it in such a way that no embarrassingly obvious mongrels are produced" -- i.e., "just don't get caught!" Thus the sanctity of breed purity may sometimes be less than inviolate in actual practice.

Population geneticists insist that limited populations under strong artificial selection, subjected to high levels of incest breeding - such as our own CKC purebreds -- simply cannot maintain genetic viability and vigor in the long term without the periodic introduction of new and unrelated genetic material. They are referring, moreover, to true outcrossing, the introduction of stock unrelated to the breeding line, not merely the use of a dog which might be from someone else's kennel but is derived from exactly the same foundation stock some generations back.

The Demise of Typological Thinking

DNA research has radically changed zoological concepts of species, subspecies and varieties. In the nineteenth century and the first half of this century it was thought that a species could be represented by a type specimen, that the vast majority of individuals of a species were virtual photocopies of the type specimen, genetically speaking, and that the genetic norm for most species was homozygous at most loci. In the mid 1960s the credibility of that idea was shattered as electrophoresis protein studies revealed extensive protein polymorphism that had not been previously suspected [Carson 1983]. Today the concept of a species in a satisfactory state of genetic health invokes a state of "dynamic balance" in which the species genome contains an array of genotypes with a high degree of heterozygosity, with multiple alleles at many gene loci. Natural selection is now thought to favour heterozygotes in a way which tends toward a high state of natural variability, preserving the greatest variety of possibilities with which a species can meet new environmental challenges. Conversely, species which have lost most of their genetic diversity, often through accidental population "bottlenecks" similar to those which regularly occur in purebred dogs, are held to be in high risk of extinction through the loss of adaptive capability. (The most notorious example is the cheetah, which is almost totally homozygous and is thought to have undergone at some time a bottleneck reducing its population to a tiny handful of specimens.)

There is no reason why dog breeds also cannot be maintained in a balanced state of heterozygosity, analogous to that of healthy wild animal species, if typological thinking in the dog fancy could somehow be replaced (or at least tempered) with population thinking. Fanciers will generally admit that no dog conforms perfectly to its breed standard. Thus the concept of the perfect type specimen, to which an entire breed ought to conform as closely as possible, is really as foreign to dog breeds as it is to animal species in the wild.

The fanatical pursuit of breed type to the exclusion of other more important factors (more important to the dog, to his owner, and to his veterinarian) has led to a distinctly unhealthy situation in most breeds. Since the majority of breeders within CKC seem to direct their efforts toward the production of a winning exhibition specimen, and since many breeders therefore breed their females to the males that do the most winning at dog shows, a situation has arisen in which continued effort to produce show winners leads consistently to greater and greater exaggerations of "type", that being the factor most susceptible to the off-the-cuff three-minute analysis of the breed ring. It is an accepted fact that strong incest breeding is the fastest route to this kind of "success"; here is one successful show breeder's recipe for "excellence" [de Boer and de Boer, DOGS in Canada, April 1994]:

 

"My approach would be to identify an outstanding, dominant stud dog. Let's call him 'Shadrack.' To improve the odds I'd buy or lease three bitches whose grandsire on the dam's side was the same as Shadrack's sire. Let's call the grandsire 'Fashion Hint.' I would breed the Fashion Hint bitches to Shadrack. Assume, in this first generation, that I get three nice bitches. For the second generation, I'd breed them to a half-brother of these three bitches (Shadrack's son, also a dominant sire). For the third generation, several 'mix and match' options include going back to Fashion Hint or Shadrack. I could also do brother-to-sister or father-to-daughter breeding." Thus the quest for more and more refined breed type leads directly to a state of advanced homozygosity, rising inbreeding coefficient, low effective breeding population and consequent impoverishment of the gene pool in most CKC breeds, through rampant uncontrolled incest breeding.

The show ring has also been largely responsible for the decline of breed purpose, working ability and temperament in a great many breeds, notably sporting breeds, herding breeds and sleddog breeds. The quick and easy gratification of blue ribbons and gilt trophies all too readily supplants the hard work necessary to preserve and advance canine working abilities. If our dog breeds are to conform to the ideal of "a sound mind in a sound body" (as advocated by the proponents of the Advanced Registry), the fancy must find some way of ensuring that less dog-breeding takes place along the lines of least resistance and cheap gratification, so that greater attention is paid to working characteristics, temperament and trainability. A balanced outlook on breed identity must be restored by integrating canine function with the ideals of conformation, beauty and "type." All kinds of dogs, toy breeds not excepted, can perform useful functions and respond to training. Those aspects of the fancy should be accorded an importance at least fully equal to that of type and conformation instead of being regarded as merely optional. For example, breeding and exhibition of utility breeds such as gundogs and sleddogs merely for sale as pets and for dog shows, with no effort made to maintain and advance their working capabilities, is an obvious abuse which must lead inevitably to mental and physical degeneracy in those breeds.

 

Abandoning Natural Selection

The breeder of domestic stock often assumes that he has abandoned the realm of natural selection and that only artificial selection plays a significant role in his breeding programme. Nothing could be further from the truth. The breeder may attempt to abandon natural selection; natural selection, however, will not abandon his stock. As one geneticist puts it:

 

"Man-imposed characteristics, however, like the flower colours and forms selected by the plant breeder, usually do not perturb the deep-set genetic variability systems of the species. Most such changes are reversible when a less restricted gene pool is restored. The 'balance' system appears to be retained by natural selection, which, perhaps paradoxically, pervades most systems of artificial selection."

(Hampton L. Carson, The Genetics of the Founder Effect. l983)

Those who attempt to set aside the balanced genomes arrived at by natural selection must struggle thereafter to attain and to maintain fitness in their stock. There is more to this than mouthing platitudes about "soundness." Artificial selection alone, such as that used to produce winning exhibition dogs, involves breeding in a way which flagrantly disregards most of the gene loci in the canine genome. Since genes assort in groups on chromosomes (a phenomenon known as "linkage"), inbreeding and selection for desired traits of superficial appearance unavoidably affect many other genes which are inadvertently selected and often fixed in a homozygous state in total ignorance of what is happening. This may be a major factor in the current prevalence of genetic diseases. Thus natural selection, baulked for a season by artificial selection, high-level nutrition, and advanced veterinary care, reasserts its primacy at a deeper and more serious level when the new genome as set up by the breeder proves flawed through genetic unsoundness, so that healthy and hardy animals can no longer be produced, however typey and attractive to the eyes of the judges the result may be.

Declining vigour caused by the inadvertent fixation of sublethal and subvital alleles will not be made up for by breed points. Fitness criteria may not be replaced with impunity by aesthetic criteria. The animal's environment is the ultimate arbiter of its fitness and will not be denied its say. You may vaccinate the dog and dose him with antibiotics, feed him with vitamins and minerals as you like, enclose him in a sterile pathogen-free laboratory environment if it comes to that! Still natural selection may not be avoided; it only emerges at a deeper level. In a sense the dog's environmental includes his own physical body; if the genes which blueprint his physiology are flawed, then the dog is doomed regardless of his beauty and classic breed type. The truth is that the "superior strain" cannot be produced by manmade breeding programmes and artificial selection; the breeder's decisions are subject to nature's veto at all times.

With what, then, will the breeder replace natural selection? If he replaces it with profit, the degeneracy of his stock will in the end put him out of business as veterinary costs and death eat up his profit margin. If he replaces it with beauty contests, in the end his beautiful contest winners will engender weaklings and degenerates. If he replaces it with screening programmes for the "elimination of genetic defects," in the end his stock will succumb to inbreeding depression as bitches fail to whelp naturally and puppies die in the nest. If he replaces it with veterinary care, in the end his stock will die prematurely of incurable cancer, or the young will fall prey to viral diseases despite repeated polyvalent vaccinations. If he replaces it with work and austerity, his stock may endure awhile longer, but in the end it will turn out to be afflicted with genetic ills that slipped through his demanding programme, or its performance will mysteriously decline as the inbreeding coefficient creeps upward. In the end, natural selection cannot truly be replaced with artificial criteria. The breeder must find a way to work with natural selection, within the framework of what is now known about the biological operation of the natural world. We in the canine fancy must begin to take lessons from wildlife biologists, from evolutionary biologists, from population geneticists.

In our quest for breed purity, the superior strain, and classic type, we have made a sad mess of our dogs - with unhappy, neurotic temperaments, epilepsy, blindness, deafness, immune system weakness, skin diseases, blood disorders, endocrine system malfunctions, crippling blood disorders, deliberate deformity, and often even the inability to reproduce their kind without breeder and veterinary intervention. How clever we have been!

Can we not now take a clear-sighted view as the millennium turns slowly over, of what we have done - of our own pitifully-flawed creation in our world of purebred dogs and, like mature, intelligent people, clear away the mess and try to do better? Can we not learn from bad experience? If we would be truly clever, we might attempt to imitate more closely the methods of nature, to work within the natural system, albeit for our own ends. That would indeed be clever. I think that that is now possible, if we would but step outside our own incestuous little purebred world and learn something of what people working in other zoological fields of endeavour have already learnt.

 

A Century of Nineteenth-Century Dog Breeding

How, then, may we set about correcting the accumulated errors of over a century of what we might call nineteenth-century dog breeding? First of all it might be wise to attempt a short-list cataloguing the errors and abuses of which we are aware, the areas known to be deficient in one way or another.

 

  • Dog shows must come high on the list. They began as an arena for the evaluation of breeding stock, they continued in the form of the "bench show" as a public showcase for purebred dogs. Both functions are now illserved if not virtually abandoned. Championship shows are now just that, mills for the production of Champions, Best in Show and Group winners, little more. They contribute almost nothing to the true welfare of dog breeds; they have few lasting positive values to offer breeders, only ephemeral fads and fashions.
  • Breed purpose and the cultivation of canine utility have a low status in the fancy compared to what one author called the glitz and hype of the show world. Those who concern themselves with the working ability of their dogs exist mostly in ghettos where little communication takes place with other branches of the fancy.
  • Obedience work, begun as a way of initiating dog owners into the fascination and technique of training one's pet to be a pleasant, well-behaved companion, has become largely ritualised and sterile. The pursuit of "Club 200" (the perfect point score) has become an obsession. Intelligent and useful training on the owner's part, intelligent obedience on the dog's part, are now beside the point. What matters all too frequently now is the minutely-perfect performance of a set ritual. Here again we find a canine ghetto.
  • The worship and exaggeration of type, as already noted, is responsible for a multitude of ills.
  • Modern registries based on a rigidly-closed studbook are throttling the genetic health of all registered dog breeds. Genetic impoverishment is now a real and present threat. Many breeds now bear a genetic load of defects which has grown totally unmanageable as their respective gene pools have become more and more narrow through imprudent breeding and selection practices.
  • Incest breeding, once a convenient tool for the rapid fixation of type in newly-registered breeds, has become virtually standard practice for those who seek success in dog breeding. The net effect has been the decimation of gene pools, widespread homozygosity and the unintended fixation of unknown scores, hundreds or thousands of alleles, many of which are proving to be harmful or lethal to the animals that bear them.
  • The CKC, born in the height of the Victorian era, seems to cling to cumbersome structures, making it difficult for the Club to respond in a timely fashion to external challenges or internal needs. The entire By-Law and Amendment structure could do with modernisation. Many members feel there is little justification for such practices (for example) as the three-year member apprenticeship proviso, under which new members (or old ones who for whatever reason have let their membership lapse for a year or more) are completely disenfranchised for anywhere from three to five-plus years (inasmuch as elections and referenda are triennial), costing the Club dearly in lost members and wasted talent. Many members also feel that Board of Directors initiatives are frequently arbitrary and undertaken hastily, with insufficient grassroots consultation, while initiatives from the general membership must go through a slow and cumbersome multi-stage routine before they can be acted upon. One feels a general atmosphere within the Club of elitism and ultra-conservatism, as if those in power felt that only they themselves, the "old hands," knew what is good for purebred dogs and the fancy, and that newer members should not be entrusted with the franchise.
  • Breed clubs seem to possess little real power to represent breeders or their breeds effectively. Special measures which they may feel essential for the health, development, and protection of the breeds whose breeders they represent must be put through the centralist CKC system and approved by the Board before they become effective; often such measures have little chance of approval because they are felt to conflict with the rigid all-breed norms of the Club. Since breed clubs have relatively little real power, they often tend to be less than fully representative of all breeders of a particular breed. Frequently they are more or less run by cliques; they waste much time and effort in wrangling and personalities, being perhaps inadequately supervised and not taken terribly seriously.
  • Breeders, as well, are sometimes far from free to make their own responsible decisions for the best interests of their own dogs and bloodlines being closely constrained by CKC Bylaws and by the Animal Pedigree Act. Little discretion is given them regarding matters such as the withholding of registration papers, delaying registration of stock until it reaches physical maturity, the introduction of new genetic material when in their judgment it is needed for genetic health, etc.

Many of the abuses and deficiencies not rooted in outmoded attitudes such as racism and elitism arise from misunderstandings of genetic realities. Let us now examine briefly a few points of up-to-date genetic theory as they relate to purebred dog populations.

 

Lessons from Population Genetics

Gene Frequencies

Much of the work of population genetics involves estimating or calculating gene frequencies, which quantify the relative commonness or scarcity, within a particular population, of alleles at a particular gene locus. If there is only one version of a gene in the population, then the entire population is necessarily homozygous for that gene. Gene frequencies are expressed as decimal fractions which must add up to unity, so a gene without alternative alleles has a frequency of 1.0. The gene frequency figure is a ratio of the number of copies of alternate versions of a gene in the population, independent of the number of animals involved and of whether they have the gene in homozygous or heterozygous form. An individual may have two copies of the same allele or it may have one or none. For example, if a locus has two alleles, and the population involved consists of fifty animals, and there are 25 copies of one allele, then the frequency for that allele is 0.25; therefore the frequency of the other allele must be 0.75, with 75 copies of it in the same population. It must be emphasised that gene frequency by itself says nothing about relative heterozygosity or homozygosity; it deals only with quantitative aspects of alleles in the population, not the diploid genotype of individuals.

 

Founder Events

Perhaps the most crucial concept in population genetics for dog breeders is the founder event, for its theory describes perfectly what takes place when a breed is "recognised" by CKC or a similar registry. Whatever may be the state of genetic balance or the frequency with which particular alleles are found in the general canine population, it all changes when a founder event occurs. In nature such events happen when individuals of a species occupy and reproduce in territory new to the species, losing contact with the source population of the migrants (as when small birds are deposited by hurricane winds on mid-ocean islands). The founder event describes the establishing of a small population, although later on it may grow to be a large one. When a finite number of individuals found a new population group, the genome of the new group will necessarily reflect the genes brought to it by the founder animals; gene frequencies within that population will reflect the gene frequencies within the founder group rather than that of the source population. In this way, when a founder event occurs, a gene quite rare in the source population may have a much higher frequency in the new population; conversely, genes common in the source population may be infrequent or even absent from the new population. It all depends on the genes of the founders! Thus a genetic defect extremely rare in the overall canine population can come to be common in a particular breed simply because one or more individuals of a small breed foundation carried that gene.

 

Hardy-Weinberg Principle

The Hardy-Weinberg Principle states that under certain specific conditions (random mating, very large population group, no mutations, absence of selection pressure, for example), the relative allele frequencies of genes at a given locus will not change from generation to generation and can be described by an equation, allowing the geneticist to create a mathematical model of gene frequencies within the population. Without trying to explain the equation and its operation here, we can still say in general that the net result is that heterozygote organisms will be much more numerous than homozygotes in a Hardy-Weinberg population. Many natural populations can be described in this way, although purebred dog populations cannot, since they are subject to inbreeding, artificial selection, non-random mating and small populations. Nonetheless, the principle has a certain significance, in that the overwhelming preponderance of heterozygotes in natural populations means natural selection tends to favour the heterozygote. Thus the natural genetic balance systems of most species include a high degree of heterozygosity [Carson, 1983]. When we as dog breeders use incest breeding and artificial selection to fix characteristics arbitrarily, we are therefore quite likely to upset the natural genetic balance of the canine species in our breed populations. Moreover, the natural preponderance of heterozygotes is rendered even more important by overdominance effects, described below.

 

Genetic Drift

Small populations, such as most purebred dog breeds, are subject to a condition known as genetic drift. This is a situation in which gene frequencies change at random from generation to generation, varying from statistical expectations because of sampling error. (Sampling error occurs when too small a number of trials departs from the expectations of probability, as when someone flips a coin six times and gets five heads and one tail - if he flipped it 600 times, the results would be close to 300 heads, 300 tails, but in a small sample, chance can cause a departure from the expected result.) This happens also when gametes unite to form zygotes in reproduction; the union of gametes is at random by hazard. A dominant black dog, whose dam was white, when bred to a white bitch should in theory produce equal numbers of white and black pups, but few breeders would be very surprised to see 2 whites and 6 blacks, or vice versa. Yet when such sampling errors occur in small populations, over subsequent generations gene frequencies can change, taking a random walk that leads finally to the loss of one allele and the fixation of the other! The smaller the population, the fewer generations this result is likely to take. In a very large population, it will not happen at all. Genes are lost and other genes fixed completely at random in this way by genetic drift.

 

Generation Time

Since in limited, genetically isolated populations such as CKC breeds a certain amount of genetic diversity is lost with each reproductive event through the action of genetic drift, inbreeding and artificial selection. The number of generations from the founder event becomes an issue. The average time between one generation and the next is a convenient yardstick to help us realise the relative rate of genetic attrition. A few instances exist in which certain bloodlines - working dogs, usually - are bred conservatively enough that the generation time is as much as an average six or seven years.

But this appears to be exceptional. Many exhibition lines seem to operate on the following model: "Phoo-Phoo" starts his show career at six months of age in Junior Puppy class, is heavily "campaigned" and has all his Championship points by ten months of age. The owners' immediate "bragging ad" in "DOGS in Canada" or the breed club newsletter recounts his triumph, adding that "puppies from Ch. (subject to CKC confirmation) Phoo-Phoo are eagerly awaited next month". In such lines the average generation time may be two years or even less. This reproductive rush has two implications: first, a greatly accelerated rate of loss of genetic diversity; second, an implicit selection for early maturity which carries with it an elevated risk of joint disease and a lowering of average longevity.

 

Effective Breeding Population

The population figure that matters in situations such as random genetic drift is not the total number of individuals alive at any one time. Nor is it even, as one might think, the actual number of individuals that contribute progeny to the next generation. Variations in breeding population from one generation to the next have a marked effect, such that the effective breeding population, especially where variations in number are extreme, tends to be only modestly greater than the lowest number. Another factor which makes a great difference and is crucially important in purebred animals is the sex ratio of successful reproductors. The effective breeding population can never be greater than four times the number of males, no matter how numerous the females may be, since gametes must come from both sexes. Thus anything that limits the number of males in use drastically restricts the effective breeding population. Overuse of popular sires is a tremendous factor in the genetic impoverishment of purebred dogs. One of the major drawbacks of the proposed CKC Advanced Registry is the virtual certainty that the existence and promotion of a few "elite" sires, titled, temperament-tested and certified "clear" of major hereditary diseases, will further dramatically reduce the effective breeding population in many breeds, causing further declines in breed vitality and viability and leading to the loss of vitally-needed breeding lines which happen not to be among the elite group.

 

Linkage Disequilibrium

Genes found on the same chromosome will fail to assort independently in accordance with Mendelian principles. Such genes are said to be in a state of linkage disequilibrium. This simple fact has a devastating effect in artificial selection, since it means in practice that when a breeder selects for or against any single-gene trait whatever, whether he is aware of the fact or not he is also selecting for or against every other gene located on the same chromosome. This is how genetic defects become rapidly fixed in inbred populations subjected to artificial selection. Since dogs have only 78 chromosomes (diploid number) but many thousands of genes, obviously linkage disequilibrium can be tremendously influential. Genes that are linked eventually become unlinked over time (except in certain special situations) through crossing over, a process whereby chromosome pairs exchange segments of their DNA structure during meiosis. The unlinking process however, is slow and unpredictable; it offers little hope of remedying the linkage disequilibrium problem in a few generations and of course is no help at all where deleterious alleles have already become fixed.

 

Overdominance

Situations exist in which a heterozygote individual enjoys a survival advantage over both the recessive homozygote and the dominant homozygote of the same gene; this is called overdominance or heterozygote superiority. As yet not much seems to be known about this mechanism and proven examples of specific overdominant genes are rare. Nonetheless this mechanism may be one reason (apart from their usually recessive nature) why genetic defects are persistently found in genomes despite their apparent fitness disadvantage in the homozygous state. While on this subject it is worth noting that population genetics offers mathematical models for various forms of selective breeding, including the selective elimination of individuals bearing homozygous recessive genes for harmful traits. These models demonstrate that the elimination from the breeding population of individuals homozygous for unwanted traits has only the smallest effect in changing the allele frequency! It has been calculated, for example, that to reduce the expression of the recessive albino gene in humans from one in ten thousand to one in one million, simply by prohibiting albino (i.e. homozygote) individuals from having children, would require nine hundred generations of such selective breeding to accomplish! This is one of several reasons why screening programmes, although perhaps profitable for the veterinary profession, are of questionable effectiveness, since they identify only affected (usually homozygous) individuals.

 

Heterosis

More commonly known as hybrid vigour, heterosis is a situation in which a cross of two or sometimes three highly-inbred bloodlines displays enhanced performance for some desired trait, as for example higher yield in corn. It works best in plant species capable of self-fertilisation, but has been amply demonstrated in domestic livestock species. It is worth noting that in practice many different inbred lines must be developed at the same time, that most of the inbred lines become so unfit that they must be discarded as they become non-viable, and that considerable random trial of different crosses must be done to establish which lines will actually yield the desired result. Although the seed-grower's methods are unsuited to purebred dogs, the overall principle is of interest, since it is thought that heterosis works because of the heterozygosity of the hybrid generation, probably through the action of both dominant and overdominant genes. Geneticists are now starting to realise that the balanced-heterozygote systems of many wild species involve a heterosis effect which gives them a high degree of fitness.

 

Inbreeding Depression

As genetic variability diminishes and homozygosity rises through inbreeding, a syndrome known as inbreeding depression sets in. It is characterised by a reduction in viability (survival of individual progeny), birth weight, fecundity (number of young) and fertility (reproductive success), among other things. Much of it is caused by the homozygous presence of rare, deleterious recessive alleles. Part of it may also be due to the relative absence of overdominant heterozygote combinations. As inbreeding depression becomes more severe, highly inbred lines tend to become extinct through the loss of ability to reproduce successfully and / or inability of the young to survive. It varies somewhat in intensity from species to species, due probably to variations in the number and nature of lethal, sublethal and subvital alleles involved. Some wild mammals which show almost no juvenile mortality when bred in captivity without inbreeding, exhibit 100 percent juvenile mortality when inbred! A survey of captive breeding records for 44 species [Ralls & Ballou, 1979, 1982] showed that juvenile mortality of inbred young was higher than that of noninbred young in 41 of the 44 species for which records were analysed.

 

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