Practical CURRENT Genetics for Dog Breeders.
For most dog breeders, as well as dog buyers, genetics is both a confusing and intimidating topic. This short article is intended to clarify some commonly held misconceptions about genetics and to offer some simplied explanations which (hopefully) will help the average person understand a few basic concepts of genetics that are important in breeding and owning purebred dogs or "registry dogs". A couple of good references written for dog fanciers are listed at the end of this article for those seeking more more information and more in-depth explanations.
THE MYTHS:
Myth#1. Purebreds are "weaker" than mutts. Mixed-breed dogs display more genetic faults and inherited disease traits than any one breed. There are endless sets of statistics to prove this idea is a myth, but they never seem to convince anyone. This is probably due to the combination of the following:
a) Sick and crippled mixed-breeds are less likely to be counted as they are less likely to be among the living, let alone among those dogs taken to vet clinic for expensive care.
b) No owner (breeder/vet) ever attributed a disease to an out-cross breeding.
c) The "Ugly Tourist" syndrome: many healthy pets live quietly on, while one sick Irish Setter or a GSD with hip dysplasia gets more than their share of the focus. Add to this that the better made pets are actually much harder to find & buy for the average pet owner, who sadly tends to, despite all good intentions, to buy from the uninformed if not our right uncaring breeder.
d) It is romantically inticing to think Nature does a better job of taking care of Her Children than corrupt man does. The fact that "she" doesn't look after any of "her individual children" is obvious only to those who study nature carefully. Sickness, death & dying is just exactly how nature winnows out the numbers to an acceptable level; cruelty by our standards is a standard event in nature-as is suffering. Nature's idea of "controlling" disease is to let the afflicted individuals be born, suffer and die.
Myth#2. Inbreeding is bad; it causes sick and unstable dogs.
This goes with the idea (also erroneous) than inbreeding doesn't occur in nature. Man's cultural taboos on inbreeding is largely behind all these myths. Inbreeding (linebreeding) & outcrossing are essentially neutral tools used to effect certain ends. It is certainly true that such a thing as inbreeding depression occurs when there is a loss of diversity among (some particular) genes in some individuals sometimes in some species, but there is also such a phenomena as outbreeding depression that occurs when you "mess with" a 'good' set of genes by introducing "new blood" into a breeding program. All this is demonstrated in wild as well as zoo populations as well as various domestic animal breeding programs. The point is you just cannot point & say "inbreeding is bad, outcrossing is good;" nature is never than simplistic. Bad breeding decisions often end in sick & unstable animals, but even the best breeding program has individuals who may fall ill. Along with this is the problem of confusing heterozygosity with heterosis (hybrid vigor). The latter is a first generation trait that occurs ONLY in the offspring of two individuals who are themselves from pure(in)bred strains; heterozygosity is a term that relates to whether a given individual has two or one kind of gene (alleles) at any given gene location (locus). The two terms don't even relate to the same level of discussion, and a hybrid is not necessarily "better." Having information on the actual animals in question is what is critical & no formula can replace that all important criteria. The results of any breeding demonstrate the skill (& luck) of the breeder. One of the most inbred lines of dogs in the world has the lowest breed incidence of hip dysplasia and the highest success rate as superior companion dogs--the seeing eye German Shepherd. Which is NOT to say "inbreeding is good;" the old breeder's saw about having to do an outcross every few generations is based on the observation that continuous inbreeding over generations can result in "inbreeding depression;" a phenomena, assumably, having to do with having too much similarity (homozygosity) among certain genes (such as immune genes). The point is one simply does not make breeding or buying choices based on single criteria or "cookbook" formulas--random outcrossing is as deadly as blindly linebreeding--smart breeders make careful selections every generation.
Myth#3. If it is a genetic trait & you have the gene, you are going to get the disease, etc. associated with the trait. This is probably one of the most commonly held & terribly wrong notions people have about genetics. Innate does not mean fated. Having a gene for some trait may be a LONG way from having the trait expressed; you won't get sick necessarily just because you have a gene for a disease. Genes don't "cause" disease; the expression of them may. Of course "carriers" are best identified & eliminated when possible from the breeding stock, but such ideal circumstances may not be available & it's critical to recognise that genetic traits are not like a scarlet letter that brands someone as a "defect," just as it's critical to recognise that we all (& all our dogs) carry defective and even lethal genes. The key, again, is selection: selection as a breeder for what defects are tolerable (i.e. those cosmetic or fashion) and which are not (i.e. those deadly or costly).
Myth#4. If the environment affects the course of a disease/trait, then that proves the trait is not genetic. This is the twin of myth #3 & just about as common. Environment is PART of the genetic inheritance of a person or dog: a certain environment is necessary for each and every gene to get "turned on" & expressed. They work TOGETHER, not in opposition. For example, if a dog with genes for hip dysplasia is fed carefully with low protein & low calcium and kept from any real exercise, this dog may express the genes later and with less obvious original bone changes than the pup who eats a ton & runs around unsupervised. Both will end up with arthritis, likely, & both EQUALLY are going to pass on their genes for this crippling disease to their offspring. The first dog is just less "honest" about what sort of genetic parent he really is. Diet & supplements can mask the effects of disease & even control them--think about adult onset diabetes which is usually controlled wholly by diet. But disease controlled by environmental manipulation isn't a cure & the offspring of dogs who need enzyme supplements, for example, are going to display the same kind of pancreatic insufficiency their parents did, even if none of these animals are ever properly diagnosed and their genetic defect isolated or even admitted. As Richard Dawkins says: "A gene's meaning is context dependent."
Myth#5 Genetic means congenital. People still confuse congenital and inherited. Inherited means acquired (genetically) from the parent(s). Congenital means present at birth. Congenital problems can be inherited. But many inherited diseases are not obvious until the animal is mature. That is EXACTLY why we still have problems getting rid of them.
Myth#6 You can buy/breed a dog without undesirable genes. This puppy buyers often demand and some breeders even will promise. Every dog alive likely carries some undesirable traits. In the breeds where this has been systematically studied, every breed individual is likely to carry for 3-5 unwanted traits(gene load). The question is less rather IF you will accept unwanted traits, than WHICH you will decree as most undesirable & which you (and your dog!) can accept and live with. Crooked tails or missing teeth sure beat heart disease and hip dysplasia---all are inherited. Which, if you had a choice, would you choose to carry in your line or have in your dog? This is rather hard for folks to swallow as they believe in myths#3-5 & think your genes are you destiny and that anything genetic is some sort of scarlet letter. We all need to learn a bit more of how biology really works & discard our erroneous ideas not based on the evidence of nature.
MYTH # 7 Genetic disease is not some sort of shame to be hidden and whispered about & it shouldn't be overlooked or forgotten. Genetic disease should be documented so the breeding of two carriers of something really scary can be avoided. One of the HUGE reasons purebreds have so many problems with genetic disease is this culture of "hide it, deny it, lie about it-while others whisper and gossip." Come on people--if we are not ashamed of what we are breeding, and if we are really concerned about the state of our 'beloved' breeds, then why are we not honestly documented the faults found out in our lines? (Pure-bred dogs need open registries, but this is another topic, sort of.) The result can be that honest breeders who admits to line faults may get bashed by their peers as well as puppy buyers, while those who hide their problems successfully often get rewarded with breedings and buyers. Let's all get a little more sophisticated, shall we?
Treat each dog like he HAS three undesirable traits & try to prioritize what is and is not acceptable; what is and is not also in your/another line. Puppy buyers, ask what the line has & expect an answer that it does have some less than wonderful things-focus on what the breeder is doing to eliminate or control them & try to find someone with a list similar to yours (of traits bad, maybe, but at least liveable/acceptable). Puppy buyers can help out by not running away from an honest quality breeder who tells you his/her line carries for this and that & running to the ostrich-sort of breeder who lives with head deeply buried in the sand. They can also help enormously by ceasing to support those who breed casually and in ignorance. It's a lack of knowledge of how to properly set up a successful breeding program more than any evil designs or other nefarious motives than is destroying purebred dogs. Sadly this decline is largely funded by pet puppy buyers who often don't seem to think the quality of the breeding program is important when buying "just" a pet. It's the buyers that keep the sellers in business & it's often overlooked that current buying practices are largely responsible for the decline in the overall quality of pets for sale.
GENETIC TERMS & their (basic )meanings.
WHAT IS DOMINANCE? Dominance is a rather old-fashioned term not much used by working geneticists anymore which describes a situation in which a gene is expressed when in a single dose. What this means is you can see the effect of the gene if the pup in question only had one parent with the trait. (And it means the pup HAD to have one parent with the trait, but could have had two). There are not a lot of examples of clear dominance & even fewer examples of undesirable traits that are clearly & simply dominant, because you simply do not breed the dog who has it and it is gone. Ticking is a typical example. You don't want ticking then don't breed, for example, to a dog who has it or at least half your pups from a clean white momma with be ticked. Nice part of simple dominance is, if you don't see it you don't have it. Of course, most 'dominant' genes are incomplete dominants, or dominants with variable expression or incomplete penetrance. Incomplete
dominance means two genes will "war" over which gets expressed and you can likely see a bit of each in the dog. A simple example is white piebald spotting; the dominant gene for self-(full)-coat color cannot cover the dog in pigment when it is not in two doses, so hybrid pups get some white markings (beyond just chest and toes) & two such "hybrids" bred together can produce white pups. Incomplete dominants give you a range & you cannot really control the exact spread of their effects. Variable expression is like incomplete dominance with the gene acting all alone: it is erratic in what it will do. Incomplete penetrance is a population comment. It means that only a certain percentage of the population that HAS the gene will show the effect of the gene. You got it, but only got an 80% chance of ever seeing its effects. In all these cases, for breeders, these are hard to control, and any example of expression must be taken for proof the gene in in the line-to act cautiously & responsiblity-and pedigrees should be so marked. These sorts of complex dominance problems cannot be treated as simple dominance is. The "responsible" party may be hard to identify.
WHAT IS SEX-LINKED? Sex or X-linked means the gene is carried on the X chromosome. So the pattern of inheritance and disease is somewhat different than for autosomal (not-sex chromosome) genes. X-linked traits are commonly seen only in males, who got it from their mother (dad gave them a Y-chromosome to make them boys). Likely half their sisters are carriers of the trait just like mom was. And you cannot tell which sister is clear & which a carrier until they have pups. Some forms of cryptorchidism (retained testicles) as well as some bleeding disorders are thought to be so inherited. DCM (cardiomyopathy) in Danes looks like it might be inherited as an X-linked, or perhaps a mitochrondrial, trait. You don't blame the daddy for this, but rather acknowledge that momma, unseen, is the author of the trait in question. (Some X-linked traits need another gene for disease to express, like epilepsy in Standard Schnauzers: in this case both parents *may* be involved in the inheritance pattern; this may well be the case for "cardio" as well. See "Polygenetic" below.) And don't forget the sisters of any such affected brother are likely carriers as they have one X gene from their momma, so pedigrees should be properly marked to reflect this, even though these sisters may never be unwell. There is another peculiar sort of inheritance that is purely from the mother called mitochondrial DNA inheritance. These are the little dynamos that give cells energy & mammals get all their mitochrondria from their mommas. Mitochondrial DNA is thought to be behind some forms of cardiomyopathy & in these cases, again, the mother is "at fault", not the dad, although both sons & daughters would more likely be equally affected.
WHAT IS A RECESSIVE TRAIT? A recessive trait is a trait for which two copies of the gene must be present for the trait to be seen. This means that is takes two to tango & BOTH parents HAD TO HAVE the gene in question. This is VERY important to understand clearly, as complex dominance and polygenetic traits must be treated (somewhat) as one treats recessive traits to rid a bloodline of a problem or mimimize the effects of a trait. BOTH parents are PROVEN (obligate) CARRIERS if they EVER produce ONE SINGLE PUP EVER with a recessive trait. This means yellow (fawn,sable, red ) or blue/brown dogs out of black animals, yellow eyes from brown eyed animals, missing teeth, cataracts and hernias (in some breeds these are simple recessives), etc. There are many, many traits on this list. So don't point fingers & hide pups with recessive traits. Contact the stud owner, mark the pedigrees properly & help make progress in your breed (and your bloodline). Mark both parents as obligate carriers, mark all "normal" offspring as 66.66% likely to also be carriers & look for common relatives of the parents who likely brought the trait down to the current generation. Don't condemn--it takes two carriers to mate to find out you got a trait--consider this an opportunity to learn more about your bloodline.You don't have to toss all the dogs on the reject pile either necessarily. If the trait is acceptable (for all it is undesirable) & liveable for the dogs, then just letting it go may be an option. If the trait is serious, then how you treat it may depend on how widespread it is in your breed. If it is rare, then best to cull these animals who are carriers from the gene pool. If it is common, then such a drastic approach may not be reasonable & you will have to use carefully marked pedigrees and/or test breedings to control the expression of the gene. After all, remember, it is not the GENE that causes the problem, but the expression of that gene.
WHAT IS MEANT BY POLY-GENETIC? Polygenetic is how many serious problems in dogs are characterized genetically. This means more than one gene is responsible for the condition's expression, and that means tracking the inheritance is more difficult and more frustrating than with simple dominants & simple recessives. Although it is certainly not precise, treating polygenetic situations as you would treat simple recessives is probably going to get you the best results as to controlling canine genetic disease, when your options for "proof" are limited. Certainly, both parents must be included as likely contributors to the disease. As a rule of thumb complex characteristics are polygenetic: hip conformation & CHD disease, head conformation and the resulting bite, construction of internal organs (that end in heart, kidney, etc. malformation or malfunction as well as normal function, of course). In some cases a single gene IS found to be the culprit, but in many cases inheritance is erratic and any particular form has not been documented, so these things get stuck into the "polygenetic" pile until they get sorted out. This does NOT mean they are "not genetic" because a certain proof of how they are inherited is lacking-that is more head in the sand tactics. If it occurs in a particular population (such as a certain breed or even bloodline) more often than in the general population, then, to be careful and conservative as a breeder, it must be treated with the caution of it being genetically inherited until proven otherwise. Anyone truly concerned with the breed is not going to dismiss the evidence it is LIKELY genetic to go on with a breeding program in denial they are carrying down certain undesirable (or even debilitating) traits.
WHAT IS CULLING & HOW IS IT USED? Culling is the removal of an individual from further breeding consideration. It is NOT necessarily killing. Any dog spayed or neutered is culled & could be called a "cull," just like any animal who never has offspring technically is a cull. Culling is selecting breeding stock, be it natural forces or breeders who choose who will produce & who will not. Culling out newborn puppies is something breeders learned from observing nature & from experience with certain early seen traits that indicate future problems. (But culling out by breeders, unlike in nature, is done by humane euthanasia, not by starvation, competition & exposure.) Puppies are not normally killed "just" for color, despite widespread myths & rumours to the contrary. Puppies are usually euthanized for one of three reasons: a) the litter has an excessive number of pups in it, b) the pup(s) in question has a trait associated with serious defects than impair a normal life, or c) the breeder is unable to find suitable homes for the puppies in question. All are acts of extreme responsibility & no breeder should be condemned for acting responsibility toward his/her pups, dam and breed. Breeders who cull out at birth are not less feeling than those who, for whatever reason (& it's too often from ignorance or emotion) "choose" not to immediately seperate out excess & defective pups. Many would argue, in fact, that breeders who cull out are in fact are simply braver, & are acting from a deep love for the breed, the pups and the dam; for to have to euthanize lives you brought into the world is never less than a terribly heavy burden. Most breeders will be faced with the need to cull out newborns at some point & some breeders (e.g. Harlequin Dane breeders) face the issue often. Culling, however it is done, keeps the breed strong by selecting only the best individuals to parent the next generation. It is a necessary breeder's tool. Culling out newborns when to keep them would have bad effects on the pup itself, on the other pups, the dam &/or the breed itself is just one of the least pleasant burdens being a breeder brings. Culling in general is used by everyone who breeds...including nature. Again culling is the natural aftermath of selecting one animal for breeding over another. It's a necessary part of any breeding program & the "culls" are NOT lesser in any sense per se: I do hope we are now at a time in history we will no longer judge anyone, animals or women for that matter, based purely on their reproductive value.
WHAT IS TEST-BREEDING & HOW IS IT USED?
Test breeding is, classically, the breeding of a suspected carrier to a dog known to have a certain trait, to determine IF the suspected carrier is a carrier. One pup affected is a definite yes answer. Less than ~8 pups without the trait, however, is little to no assurance the suspected carrier can be cleared of its suspect status. Very few breeders actually & deliberately keep & breed a dog with PRA or vWD, although this is exactly how English breeders of Labradors practically deleted the genes for PRA out of their bloodstock. Test breeding is a most effective tool & can also be used "retroactively" on any breeding you do. For example, when a dog at public stud develops PRA. If you bred to the dog & your stock remains clear, especially when it was suspect, then this can help provide info on the status of the dogs in question. The same sort of general information can be gathered and used when a breeding produces an affected individual to at least identify carriers. The trick is to USE the info, not to bury it, or condemn the breeder who cared enough about their breed to announce it publicly when a dog of theirs is found to carry a serious defect. Thanking them would make more sense. This way, the next generation of breedings can be done with more information and, therefore, with potentially better results. As more & more genetic marker tests become available, we may more easily be able to identify carriers. What will we do then about the information we have?
INBREEDING, LINEBREEDING, OUTCROSSING-WHICH IS BEST?
To paraphrase the great Laura Kialenaus, what matters is the quality and qualities of the dogs in question; not the "formula" by which they are bred. Linebreeding is often touted as some sort of special way to get good dogs. Linebreeding is simply weak inbreeding, so carries all the problems of both outcrossing and inbreeding & simply gives people uncomfortable with the idea of inbreeding a way to comfortably inbreed to retain desired characteristics. The degree of relationship, in any case, does not necessarily indicate the amount of genetic material shared. Everyone has seen two "identical" cousins, as well as brother-sister pairs as unlike as night and day to illustrate this point. Again, sophisticated decisions, based on in depth knowledge of what those pedigrees mean, are needed. To breed two dogs together (wisely and for good results) you must have intimate knowledge of the dogs in their respective pedigrees & what characteristics they likely share.
Outcrossing: used to be (still is?) the time honored way to deal with a genetic problem. When your line shows a problem, breed out to "get rid of it." Except you don't --it is still there, now just hidden--along with whatever the sire's family also contributed "in secret". It may be back to haunt you (and your puppy buyers) later on. Document what you got & what you are getting. Outcross when you need a "hybrid state" for best expression. Outcross to bring things into your line you cannot find within it & know some unseen "travelers" will accompany the traits you desire. The best outcrosses may not really be outcrosses at all, as two separate families with similar styles & traits are merged together; different names, but maybe the same 'good' genes for good heads are present, for example, in both families. These trait or type breedings (assortive/assortative matings) are a strategy to get the "good" genes for a trait without doubling up on a specific individual. They have the extra added advantage to the breed (if not your specific breeding) of possibly helping to preserve diversity in the population. Of course, many "outcrossings" wouldn't be that if extended pedigrees were viewed: many breeds & many major & successful bloodlines in a breed go back to a handful of the same relatives (& this is not necessarily a bad thing, if the dogs were good). Again, information on the dogs in question is so necessary.
Inbreeding: brings skeletons out of the closet. They were already there, but now you have to face them. It can be a great tool for finding out what you didn't know about your bloodlines, but it takes a steely heart to face up to what you find. It also takes great dogs to breed close as you are fixing traits fast and hard. The closer the breeding, the better the two dogs must be to make it worth it. Call weak inbreeding linebreeding if you like, but breeding dogs closely related is technically inbreeding (although there is a good argument to separate the two), as the point is to double-up on desired family characteristics by doubling up on the desired genes. But most everything recessive in the family eventually pops up, good & bad, when line-breeding over generations, so eventually blind line-breeding leads to the same bottleneck as intense inbreeding; it just takes longer to get there. The bad news about inbreeding is that the homozygous sought may be found. In other words, you are trying to double up on genes for good heads or strong hearts, but also double up on the genes in the immune system & that can lead to inbreeding depression. So be careful what you wish for when inbreeding, especially repeatedly &/or tightly.
Brackett's Formula: "Let the sire of the sire become the grandsire on the dam's side." Lloyd Brackett's prescription for linebreeding has proven very effective WHEN the dog linebred on is a truly superior example of the breed_&_can correct the weaknesses in the bitch/pedigree in question. Pat Craige Trotter in her book "Born To Win" discusses some successful strategies & possible formulas for particular situations, but no "cookbook approach" to dogs will ever work: breeding dogs is an artful science or a scientific art and takes both talent and study to properly accomplish. Outcrossing can be like sweeping problems under the rug (if it is really an outcross that is done). The pups from two such lines now carry some mishmash of what either or both parents brought down out of their families.
KENNEL BLINDNESS. All breeders have their favored characteristics and pet peeves. All are willing to sacrifice the perfection of certain traits to consistently achieve others they feel more important. This "worldview" on their chosen breed(s) leads to a style and the emphasis of certain traits within the correct type that breeder will be known for (e.g. size, headtype, longevity etc.). That many breeders have deliberate styles of dogs is good for the breed; it preserves the variety & strength of the breed. But many breeders fall foul of their own likes & dislikes, especially at the beginning when they know little about the breed and later on, as the years pass and they achieve some success, having now looked at the style they chose to breed so long they think of it oftenas the breed itself. If this quality is combined with an intolerance for one's rivals and/or for the faults least liked and virtues most admired, a good line of dogs will dwindle down to be more memory & reputation than a still truly vital line producing excellent dogs. Kennel blindness is also an almost universal trait of the "Sour Grapes Society;" those "wannabees" in a breed who have a thousand excuses for why their dogs don't succeed, all of them to due with the faults of other people and other people's dogs. It is also a major trait in so-called "pet breeders" who tend to not self-educate about the breed at all, so don't really know much about the breed they may well adore. They generally let their love for their pets blind them to their breeding worth...or lack thereof.
BREEDING "UP." This usually means using a well-known dog on a poor quality bitch in the hopes her offspring will succeed where she failed. Stripped down to this raw definition it's obvious what a bad idea this is. Stud owners should not let themselves be talked into breeding to sub-standard bitches & novices shouldn't attempt to get better pups this way. However it happens all too often. But the outcome is nearly always the same: the proud owners of those new pups find they are not enough better than their mother to be competitive & the stud owner finds the reputation of the sire is damaged by those who see these poor quality pups as typical of what he produces. Stud owners shouldn't allow themselves to become this kennel blind. Worse is the idea of starting out with admitting "pet" animals & hoping (?) to breed something better somehow. This falls under the old saw about silk purses & sows' ears, but incredibly is still attempted _&_ defended as a way to start in dogs. You just cannot "get there from here." Surely there are more than enough dogs in this world without starting out deliberately to make mediocre litters. Enough said.
BREEDING PEDIGREES (& other records), POPULAR SIRE SYNDROME & MATADORS. Too many people breed "paper tigers:" they breed dogs who are relatives of a famous dog as if they were somehow magic or just as good, they breed to a dog's popularity, it's show record, it's fame, or even to their best friend's dog or the closest, most convenient dog. It's astounding as much as has been written in the last century about the perils of breeding "paper" that it is still done so often. A sire is only as good as his get & his get will equally reflect the bitches taken to him. It's no use to hope the one (or ten) good pup(s) you saw out of him will happen to you when your bitch isn't like the dams of those pups. It's even worse to think that his fame will arise in his litters; one cannot take the parents' show records into the ring to convince the judge of the merits of their offspring. Nor can you honestly think that a dog having "famous" grandparents gives you a reason to breed. Further, when certain sires are overused in a breed, these popular sires become a potential danger to the breed. If their influence is too widespread, then it becomes hard to breed away from them. Diversity of style as well as genes is lost in a breed. If said popular sire turns out to have a damaging genetic flaw, the Popular Sire Syndrome has now spawned a Matador--a dog whose late-recognised fault is now widespread enough in the breed to "kill" it. This is all bad practice. Selection is lost when a pedigree or fame is the deciding factor for the choice of breeding partner. It's ill-educated to breed to an ad or a reputation. It's a doomed effort (except for sales) to breed for convenience or to "see what happens." And terrible dogs are made by blind line-breeding: faults are fixed in & a good line is eroded over time. Each breeding musts be done seeing the sire and dam as crowded in by their respective families when it comes to flaws, but standing alone when it comes to what virtues they can even potentially offer. There is, again, no recipe for breeding dogs & no substitute for a well-trained eye.
PRESERVING QUALITY & GENETIC DIVERSITY IN A BREED. As Dr. Jerome Bell so succinctly put it: "It is the varied opinion of breeders as to what constitutes the ideal dog, and their selection of breeding stock that maintains breed diversity." The current problem of erupting genetic disease, as far as it applies to pedigrees & breeding, reflects two trends. One is a problem of the "Matador," that is the "Popular Sire Syndrome." When all run to breed to a winning dog, or some dog or bloodline, (for whatever reason, be it convenience, ignorance or perceived value), genetic diversity can be lost. But indiscriminate universal assortative matings is not the answer to this problem & can actually reduce genetic diversity in the breed by "homogenizing" gene pairs across the whole breed. Outcrossing cannot solve the problem of genetic disease anymore than inbreeding is the cause of it. However "type" breeding, that is, the mating of two animals of similar looks, not similar pedigrees, CAN effect one particularly good thing which is the take-home message of "diversity breeding": since the number of genes involved
with creating a certain "look" are much less than the likely number doubled up with linebreeding (esp. "blind" linebreeding, time and again, on some "famous" relative), the loss to the breed of heterozygousity is slowed and the individual dogs are arguably more safe from various line defects...while still having "type."
The other major problems in dogs today as to disease has little to do with hobby ("show") breeders & is largely a problem of casual breeding. Casual breeding produces more than three-quarters of all registered dogs in the USA & assumably (nearly) 100% of mixed-breed litters. as a result of the low investment & high profitability (not just in money) that dog breeding brings to the average American household. There is a clear cultural support for anyone & everyone breeding their own pet, and this license runs counter to the serious study & self-education process necessary to breed dogs well enough to avoid bad temperaments and worse health problems. That so many pet buyers do not clearly see this means casual breeders are able to enjoy having litters, & be certain of sales, even if their only credentials are that they love their dogs. These litters, despite the buying public's perception & causal breeder's claims, suffer often from major genetic problems they continue to pass along _and_ they are often indiscriminately inbred, as they are usually exclusively local (or narrowly regional) breeding programs, often with the whole breeding population sustained by a couple of friends. What is needed is educated, dedicated, honest breeders & scrupulous selection. Breeders need to know the dogs they are using in their breeding programs & need to know them intimately. Each needs to have a clear priority of what they cannot live with & what they cannot live without. (And ideally each would clearly announce this somehow so others are clear on their priorities before they buy or breed from them.) A variety of styles, of lines, of sub-populations, criss-crossing, separating & then, again, coming together in a wonderful breed mosaic, is the best recipe for maintaining type, health, temperament _ &_ diversity in any breed. And for all that "diversity" is a buzzword of fashion right now, it isn't at all a new idea, just a new term for the notion of having a variety of bloodlines within a breed. (Note also that diversity does not necessarily equal outcross.) What is needed in most all breeds is for more good dogs to be rooted out & recognised, despite their lack of glamour & dazzling ads. (That & for America to get serious about dog breeding & treat it with the gravity it deserves.) It would also help if more folks would work together to preserve bloodlines and create new ones by judicious crosses, so that variety would be preserved. For this more people will have to get educated about the history and styles of their breed; too many today simply breed to some current fashion )or market!), oblivious to the fact what they are seeing is simply fashion and not "the" standard for the breed.
SPORTS do not generally produce good offspring. Sport is a term many breeders no longer use, but is a useful idea. A sport is the odd good dog in a litter that is otherwise uneven. It is traditionally the occasional decent dog found in a litter from an unlikely background and breeding. Usually such dogs are the fortuitous result of a mixed litter from a casual breeding, & the people who breed to the dog are the ones who pay the price for his mixed-up, casual pedigree & genetic background. But sports can come about from breeding "paper" not dogs; from trying to breed "up," from blind line-breeding, or any convenience or accidental breeding. A sport is a dog by definition, almost, who is unable to reproduce himself, for all his good looks. Very uneven litters & erratic littermate traits result and are certainly not helpful to a breeding program & make it hard to track both good and bad traits with any likely success. Sports can play another negative role in the breed if they become famous showdogs (or just popular sires for any reason). Not only are they breed despite the fact they are indifferent sires, their every mediocre relative is used with great enthusiasm as the family is all thought consistently "good" (instead of seen for the inconsistent lot they really are). Breeding "paper" instead of dogs has a consistently poor result, but breeding dogs who cannot reproduce themselves should be recognised as a poor practice as well.
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