Dog Breeds Articles | DOGS

By: Genetic Structure of the Purebred Domestic Dog Science

Dogs have been selectively bred for thousands of years. Initially the selections centered on domestication and useful qualities such as hunting ability. Later, dogs were also selected to give attractive and distinctive forms resulting in a vast variety of types. The point at which a new variety becomes a breed can be difficult to decide. National kennel clubs often differ in their recognition of breeds and rare breeds might not be recognised outside their home country. Usually, only dogs recognized by a kennel club are eligible to compete in the club's dog shows and dog sports, although many dog sports allow any healthy dog to compete regardless of the breed.

The oldest of all dog breeds are commonly believed to be the Pharaoh Hound and Ibizan Hound, which resemble the ancient Egyptian dogs drawn on tomb walls more than 5000 years ago.

Today, approximately 150 breeds are officially recognized by the American Kennel Club, which assigns each breed to one of seven groups or a miscellaneous class, based on the uses for which the breeds were originally developed. The modern categories include breeds that have been around for fewer than 500 years. However, the domestic dog species (Canis familiaris) includes more than 400 breeds that differ in their appearance (size, coat length, and color) and behavior (guarding, herding, and hunting).

Many traditional dog breeds recognized by the main registries are said to be "purebred". Only individuals whose parentage consists only of other purebred examples of the breed are regarded as part of that breed. This concept has caused controversy both because of the difficulty of regulation and because of the possible genetic consequences of a limited population. Recent work has been done to genetically classify the various breeds, with some surprising results regarding the estimated age and interrelations of the breeds.

Fourteen ancient breeds of dog have recently been identified through advances in DNA analysis. These breeds of domesticated dog show the fewest genetic differences from wolves. The breeds are geographically diverse, including dogs from Siberia, Japan, Alaska, China, Tibet, and Africa. The identification of these fourteen "Ancient" dog breeds was established in the article "Genetic Structure of the Purebred Domestic Dog" in the journal Science [1], Volume 304 (May 21, 2004).

The following are the dog breeds listed as ancient in the published study along with their countries of origin:

Afghan Hound (Afghanistan)
Akita (Japan)
Alaskan Malamute (United States (Alaska))
Basenji (Congo)
Chow Chow (China)
Lhasa Apso (Tibet)
Pekingese (China)
Saluki (Egypt)
Samoyed (Siberia)
Shar Pei (China)
Shiba Inu (Japan)
Shih Tzu (China/Tibet)
Siberian Husky (Siberia)
Tibetian Terrier (Tibet)

Generally, before a type of dog is recognized as a breed, it must be shown that mating a pair of that type always produces dogs that have the same characteristics as the parents, usually both in appearance and in behavior. This is known as breeding true. There are many issues concerning what is considered breeding true. For example, Flat-Coated Retrievers must always be black; however, yellow coats occur occasionally in some litters. Kennel clubs do not recognize the yellow dogs as legitimate members of the breed. Today, such dogs are neutered and placed in homes as pets rather than risk becoming breeding pairs. As another example, a breeding pair of Belgian Shepherds of the Groenendael variety can produce puppies of the Tervueren (brown) variety; the AKC considers the varieties to be different breeds and, therefore, the brown puppies are invalid and undesirable dogs, whereas the Canadian Kennel Club (CKC) considers them simply to be different varieties.

A mixed-breed dog (also called a mutt or crossbreed) is a dog that is a mixture of two or more breeds. Since, except for extreme variations in size, dogs interbreed freely, mixed-breed dogs vary in size, shape, and color, making them hard to classify physically. Historically, the foundation stock for purebred dogs have been selected from some mixed-breed population. The Golden Retriever is such an example. Some American registries and dog clubs that accept mixed-breed dogs use the breed name All American, referring to the United States' reputation as a melting pot of different nationalities.

All possible body shapes, ear types, and tail styles can appear in mixed breeds. Extremes in appearance, however, such as the flattened face of the English Bulldog or the extremely curled tail of the Pug, seldom survive even the first crossbreeding. Mixed breeds also tend to have a size between that of their parents, thus tending eventually toward the norm.

Mixed-breed dogs can be any size, weight, or color, but some colors are more common than others. No matter their parents' colors, mixed breeds are often a light-to-medium brown or black, frequently with a white chest and other white markings. The light-brown coat is sometimes called yellow, as personified by the fictional dog Old Yeller. A brown coat with black across the top and sides is also quite common.

Predicting the adult appearance of a mixed-breed puppy is difficult. Even purebred puppies do not look much like the adult dogs they will become, and with mixed-breed puppies it is nearly impossible. If one knows the breeds of the parents, some characteristics can be ruled out; for example, a cross between two small purebreds will not result in a dog the size of a Great Dane. Some breeds tend to pass on their physical traits to mixes more than others. Border Collies and some Spaniels, for example, often produce offspring with similar coats and ears. The crossbred offspring of German Shepherds usually have Shepherd faces and other characteristics.

With each generation of indiscriminate mixing, the offspring move closer to the genetic norm. Dogs that are descended from many generations of mixes are typically light brown or black and weigh about 18 kg (40 lb). They typically stand between 38 and 57 cm (15 and 23 inches) tall at the withers.

Guessing a mixed-breed's unknown ancestry is difficult for even knowledgeable dog observers, because mixed breeds have much more genetic variation than among purebreds. For example, two white mixed-breed dogs might have recessive genes that produce a black coat and, therefore, produce offspring looking unlike their parents.

The theory of "hybrid vigor" suggests that dogs of mixed ancestry will be healthier than their purebred counterparts. In some cases this might be true, because inbreeding among purebreds has made some breeds prone to various genetic health problems. Mixed-breed dogs are less likely to have certain genetic disorders, as their parents come from a more diverse genetic pool so that detrimental recessive genes are less likely to occur in both parents. For example, large dogs such as German Shepherd Dogs often suffer from hip dysplasia. Mating a German Shepherd carrier of the faulty gene with a dog from a breed not known to suffer genetic hip problems reduces the likelihood of producing offspring with the problem. On the other hand, breeding the Shepherd with another Shepherd whose ancestors do not have the genetic problem also has this beneficial effect.

In a recent article published in the journal Science,  studied the genetic relationships among a diverse range of domestic dog breeds. Their analysis revealed that the degree of genetic differentiation between dog breeds is much higher than previously thought, and in fact higher than that found between human populations on different continents!

Given that most modern dog breeds have existed for fewer than 400 years, and that pure-breeding tends to restrict the genetic pool for a given breed, it is surprising that dog breeds are, in fact, genetically distinct. This is good news for the purebred enthusiasts among us because it goes against the notion that mixed-breed dogs are somehow more genetically vigorous.

Some purebred dog breeds do have difficulties associated simply with the exaggerated physical traits of the breed. For example, the French Bulldog has such small hips and such a large head that artificial insemination and Cesarian section are usually required to produce puppies. Crossing such a dog with another breed will likely produce dogs without these reproductive difficulties, although most authorities on dog populations discourage reproduction among crossbreeds and mixed breeds because there are already so many purebreds available for adoption in addition to mixed breeds.

There is no guarantee of good genetic health of any dog, purebred or otherwise, as not all damaging genes are recessive. Also, of course, purebred and mixed-breed dogs are equally susceptible to nongenetic ailments, such as rabies, distemper, injury, and infestation by parasites.

It's important to note that all dog breeds are man-made creations: dogs were traditionally bred for specific functions. All existing dog breeds began as mixed breeds, either by random occurrence or by deliberate crosses of existing breeds. Encouraging desirable traits and discouraging others, breeders sought to create their ideal appearance or behavior, or both, for dogs, and, additionally, to ensure that the dogs could consistently produce offspring with the same appearance or behavior. Some consider mixed breeds undesirable, but mixing breeds can lead to desirable results, especially in the hands of an expert breeder. On the other hand, inexperienced crossbreeders can produce disastrous results. For example, the offspring of an obsessive Border Collie and an energetic, destructive Terrier could be dogs whose behavior is so erratic as to make the dogs a liability.

Both purebred and mixed-breed dogs can excel at dog sports, such as obedience, dog agility, flyball, and frisbee. Often, highly energetic mixed-breeds are left with shelters or rescue groups, where they are sought by owners with the caring, patience, and drive to train them for dog sports, turning unwanted dogs into healthy, mentally and physically stimulated award winners.

Historically, dog shows and dog sports excluded mixed-breed dogs from competition. While this tradition is changing, some sports still remain open only to one breed of dog, such as greyhound racing, or to one type of dog, such as sheepdog trials open only to dogs of known herding ancestry. In the latter case, herding organizations now sometimes accept mixed-breed dogs who have evident herding-dog ancestry, such as Corgi mixes or Border Collie crosses.

Until the early 1980s, mixed-breed dogs were also generally excluded from obedience competitions. However, starting with the American Mixed Breed Obedience Registry (AMBOR) and the Mixed Breed Dog Club of America (MBDCA), which created obedience venues in which mixed-breed dogs could compete, more opportunities have opened up for all dogs in all dog sports. Most dog agility and flyball organizations have always allowed mixed-breed dogs to compete. Today, mixed breeds have proved their worth in many performance sports.

Some kennel clubs, whose purpose is to promote purebred dogs, still exclude mixed breeds from their performance events. The AKC and the FCI are two prominent hold-outs. However, the AKC does allow mixed breeds to earn their Canine Good Citizen award.

In dog shows, where dogs' conformation is evaluated, mixed-breed dogs normally cannot compete. For purebred dogs, their physical characteristics are judged against a single breed standard. Mixed-breed dogs, however, are difficult to classify except according to height; there is tremendous variation in physical traits such as coat, skeletal structure, gait, ear set, eye shape and color, and so on. When conformation standards are applied to mixed-breed dogs, such as in events run by the MBDCA, the standards are usually general traits of health, soundness, symmetry, and personality. The Kennel Club (UK) operates a show called Scruffts (a name derived from its prestigious Crufts show) open only to mixed-breeds in which dogs are judged on character, health, and temperament.

The mature appearance and behavior of purebred puppies is more predictable than that of mixed breeds, including cross-breeds. With purebred dogs, the genetic variations are well documented and a breeder has a fair estimation of what type of offspring a given pair will produce. Even still, there is variation within breeds; for example, two champion sheep-herding Border Collies might produce offspring with no interest in sheep herding.

Mixed breed dogs are, on average, no more intelligent than purebred dogs, and both sets feature both slow learners and dogs with high learning capacity. For example, Benji, the hero in a series of films named for him, was a mixed-breed terrier. However, it is more difficult to predict the trainability of mixed-breed dogs when they are very young. Most Golden Retrievers are eager to please, but a mix of a Golden with the independent Siberian Husky could inherit either dog's trainability—or you could get a dog with the endurance and athleticism of the Siberian and the trainability of the Golden.

Many people enjoy owning mixed breeds, valuing their unique appearance and characteristics; while dogs of some breeds, such as the Tervueren, exhibit little variability of appearance, mixed-breed dogs exhibit often unique appearances. Although some dog owners have a specific breed of dog they wish to acquire, and will never accept a mixed breed, many others enjoy mixed-breed dogs that exhibit characteristics similar to their favorite breeds; in fact, with a mixed breed, they can enjoy some aspects of appearance and personality of two favorite breeds with a single dog.

There is usually an abundant supply of mixed-breed dogs wanting owners, available at negligible prices, while pedigreed dogs can cost hundreds or thousands of dollars and reputable breeders can be hard to find.

Some owners value a dog's pedigree as a status symbol and, therefore, have no use for mixed-breed dogs, whose market value is effectively zero; others particularly appreciate the physical or behavioral traits of certain breeds; still others ignore pedigree and, instead, value a dog's personality and health. In short, most dog owners believe that their dog's breed—and specifically his or her own dog—is the best sort of dog there is.

One of the best sources for both purebred and mixed breed dogs is your local animal shelter. The cost is low and many of the animals are housebroken.