NewGoldPawsWhiteBckgrnd

 

MainTopicHeader

Practical Genetics for Dog Breeders

THE MYTHS:

Myth#1. Purebreds are "weaker" than mutts.  Mongrels 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 convinceMediumGirlDNA anyone. This is probably due to the combination of the following:

a) Sick and crippled mongrels 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 a mongrel's 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 and buy for the average pet owner, who sadly tends to, despite all good intentions, to buy from the uninformed if not outright uncaring breeder.

d) It is romantically enticing 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) that inbreeding doesn't occur in nature.  Man's cultural taboo 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 and 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 saying 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 and 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 and eliminated when possible from the breeding stock, but such ideal circumstances may not be available and it's critical to recognize that genetic traits are not like a scarlet letter that brands someone as a "defect," just as it's critical to recognize that we all (and 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 and 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 and 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 and 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 and think your genes are your destiny and that anything genetic is some sort of scarlet letter.  We all need to learn a bit more of how biology really works and discard our erroneous ideas not based on the evidence of nature.

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 documenting the faults found out in our lines?  (What we need is open registries, but this is another topic, sort of.)  The result can be that honest breeders who admit 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 and 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 and expect an answer that it does have some less than wondeful things-focus on what the breeder is doing to eliminate or control them and 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 and running to the ostrich-sort of breeder who lives with their 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 that 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 and 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 and even fewer examples of undesirable traits that are clearly and 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 will 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 and 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 as proof that the gene is in the line-to act cautiously and responsiblity-and pedigrees should so be 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 "Polygenic" 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 and 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 and 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 polygenic 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 and 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) and 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 it is 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 and 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 POLYGENIC?   Polygenic 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 and 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 "polygenic" 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 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 and deliberately keep and 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 and 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 and 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 and 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 characterisitics.  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 and 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  and 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 and 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 and many major and successful bloodlines in a breed go back to a handful of the same relatives (and 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 seperate 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 and/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 and can correct the weaknesses in the bitch/pedigree in question.  Pat Craige Trotter in her book "Born To Win" discusses some successful strategies and 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.

CHROMADANE/chromadane@juno.com/http://www.flash.net/~dby/JP Yousha.1999. Updated 2000.

Kennel Blindness |  Genetics |  Babies & Bath

footerBottomLeftBurgundyBlack

footerBottomBurgundyBlack

footerBottomRightBurgundyBlack