Practical Genetics for the Breeder

What is the practical study of genetics about?

Breeding is, of course, about producing glamorous, sound dogs with good temperament, whatever that is considered to be for the breed in question. These things are, of course, the outer, visible, obvious characteristics of a dog. Breeding also (I hope we can all agree) should be aimed at producing healthy, long-lived animals which will be around to enjoy life and delight breeders, buyers, and onlookers for many years, subject to the limitations of the breed (I don't think we can expect Bernese Mountain Dogs to ever equal Toy Poodles in average lifespan). Vigor, health and longevity are, unfortunately, not always so evident to the eye when a breeder is making breeding decisions or a judge is deciding on placements.

Most pure breeds have at least one or a few genetic diseases that occur at high frequencies, such as mitral valve disease for Cavalier King Charles Spaniels. MVD, we are informed, occurs in Cavaliers at 21 times the average rate for other dogs, and the disease has much earlier onset and much faster progression in Cavaliers to boot. It would be nice to reduce this rate of occurrence. I'm sure that any breeder can name one or two problems of overwhelming concern for her breed, of which the same could be said. The pet-buying public is hopefully becoming more informed about these issues as well, although I haven't noticed much of a decline in puppy mill production lately, so perhaps not.

Every good breeder surely agrees that it is possible to breed for a good front or a typey head even though these traits are complex. Good breeders routinely juggle a plethora of extremely complicated traits having to do with skeletal structure, size, coat color and texture, and temperament in their breeding programs; and many do so with only the most rudimentary understanding of the underlying genetics behind those traits. Look at Mary Roslin Williams, in her excellent book Reaching for the Stars, for example. Good breeders do this with good success, which is why there is a difference in type and style between puppy-mill dogs and well-bred dogs and a difference again between the animals novice breeders produce and the ones produced by master breeders.

Why then, if breeders routinely strive to improve complicated phenotypic traits, does the control of canine genetic diseases appear to be so difficult?

There are several reasons:

First, please keep in mind that there is no way to tell whether genetic problems are getting worse in purebred dogs -- whether there is more trouble with genetic diseases now than there used to be. That is the impression a lot of people have, but this impression might arise because a lot more is known now about genetic diseases than used to be known, or because diagnostic criteria have changed, or because people talk a lot more about the subject than they used to, or because more breeders try to save affected puppies, or because dogs in general are living longer than they used to (and more closely with people) and therefore are more likely to suffer from a genetic problem at some time during their lives (and have a problem noticed).

Second, genetic problems may appear hard to solve if no one, or very few people, are trying to solve them. This is the case with commercial breeders and with, by definition, backyard breeders. It is, unfortunately, also the case with those breed clubs that, and any breeders who, pay lip service to health but refuse to share necessary information with one another or take even the most basic steps to advance the genetic health of their breeds. It is also the case that genetic problems will appear difficult to solve when breeders who are trying to be responsible nevertheless lack the basic knowledge of genetics necessary to take effective steps to reduce the occurrence of genetic problems in their breeds. In none of these cases are specific genetic problems necessarily hard to solve in theory. Rather, outside factors are preventing solutions from being understood or applied.

Third, some genetic problems are hard to solve because they just are hard to solve. Genetic problems that are genetically complex -- that are polygenic or lack complete penetrance or arise from different, distinct genetic syndromes or are late-onset -- are just hard to work with in a breeding program. Disease traits unfortunately tend to be a lot harder to work with than even the most complicated and recalcitrant type traits. Any experienced good breeder can assess the type, structure, and temperament of a puppy or a young dog -- and can do so at an early age, before that animal is bred. It's by doing just that that a breeder decides whether to keep this bitch or that one, and whether to breed her to this stud or that one.

It's much harder to assess the genes an animal possesses that might later cause it to develop heart disease, sebaceous adenitis, hip dysplasia, hypothyroidism, syringomyelia, epilepsy or cancer. Late-onset diseases are absolute hell to deal with in a breed -- particularly when those diseases are polygenic, such as MVD. Problems like epilepsy, where similar clinical signs are created by many different routes, are at least as bad. A reliable genetic test may exist for a simple single-gene disease, solving the problem, but there's no need to hold your breath waiting for genetic tests to be developed for polygenic problems.

There's no good excuse for allowing a simple disease like copper toxicosis or type A hemophilia, which can be diagnosed at an early age, to seriously impact the health of a breed. But late-onset, complicated, polygenic, or multiple-cause problems are a whole 'nother kettle of fish. Efforts to control a complicated disease can cause the emergence of other, unexpected problems -- there is some evidence that the vigorous attempts to control MVD in Cavaliers is one factor that has led to the emergence of syringomyelia as a problem in the breed. I'm sure we'd all have loved to trade MVD for a nice, simple, one-gene, non-lethal problem, but we didn't get to choose, and the discovery of SM in the dogs of your breeding program is nobody's idea of a good time.

Controlling genetic diseases in dogs is, however, possible. It has been done. As of 1998, Padgett reported excellent progress by a particular Northwest Collie Club in reducing the incidence of Collie Eye Anomaly (probably polygenic, according to a persuasive argument by Hutt) and Gray Collie Syndrome (probably a simple recessive) in their dogs; the Portuguese Water Dog Club of America has had very good success working with the Portie storage-disease problem (simple; that is, single-gene) and also with hip dysplasia (polygenic). The Alaskan Malamute Club of America took on Malamute dwarfism (simple) and substantially reduced the incidence of that problem in their dogs. (Padgett, Control of Canine Genetic Diseases, 1998.)

None of these success stories took huge amounts of time. According to Padgett, each concerned group or club took only a few years to achieve each of these aims. What it took was a cohesive effort by each group, with individuals pooling their information and being honest with one another. It also took a reasonable understanding of how genetic inheritance actually works. Commitment is not enough. An accurate understanding of how to manage genetic problems is essential. According to Dr. Jerold Bell, there are clubs that have actually made their breeds less healthy by concerted but misguided attempts to eradicate particular problems. This occurs when a universal focus on a single trait to be eliminated causes, first, the removal of too many quality dogs from the gene pool of the breed; or second, the overuse of a small number of studs known to be free of that trait. Or both. All dogs are carrying something. Those studs clear of trait A are certainly carrying something. Breed clubs that pursue this kind of strategy find out just what that was a few generations down the road when it pops out in the descendants and is suddenly widespread.

If a wonderful animal turns out to be a carrier for something unpleasant, or worse, affected, does that mean that this dog needs to be discarded from your breeding program? Do his siblings and offspring need to be sterilized and placed out as pets? Is his whole line contaminated, forcing you to start over? Are you tempted to pretend the problem isn’t even there so that you won’t have to take unpleasant steps – the “Oh, my dog never produces problems” syndrome, that everyone seems to agree is so common?

None of this necessarily needs to be done. Practical genetics is all about preserving and improving your lines while also cleaning them up.

So. The goal for a Practical Dog Breeder is to reduce to a very low frequency as many genetic problems as possible from her stock while simultaneously continuing to move forward with her breeding program. "Moving forward" also includes reducing genetic problems that are not diseases, such as straight shoulders, undershot bites, or popping hocks, while improving or maintaining glamour and style as well as facets of the line that aren’t visible to the naked eye, such as longevity, good maternal instincts, and temperament. What the Practical Dog Breeder wants – that golden glow I'm sure everyone is reaching for at the edge of the horizon – is to produce beautiful, typey, sound, sweet-tempered, beautifully-moving dogs that are not carrying any of the common genetic problems that plague the breed and that live long, healthy lives.

To achieve this laudable goal, it really is necessary to understand something about genetics (as well as something about canine structure and something about breed type). This is exactly the case where a little learning is a dangerous thing. Breeders who understand a little genetics run the risk of making things worse for their dogs and their breed. This is one of those cases where more really is better.

So. On to the actual practical genetics, as promised in the title.

I) Is the trait genetic at all?

II) If so, what is its mode of inheritance?

III) Dealing with different modes in your breeding program.

IV) How many ancestors does my dog have?

V) Consideration of specific cases.

VI) Is inbreeding inherently bad for health?

VII) Hardy-Weinburg and the practical breeder.

VIII) Heritability Doesn't Mean What You Think It Means.

IX) A Serious Plea for Scientific Thought in Dog Breeding.