Veterinary Researchers Study Ancient Dogs' DNA
University of California, Davis, School of Veterinary Medicine researchers -- trying to stamp out inherited diseases in purebred dogs -- are tracing some ancient branches of the canine family tree.
Scientists at the school's Veterinary Genetics Laboratory are analyzing DNA samples of the domestic dog's wild cousins from around the world -- including Alaskan wolves, Australian dingoes, Carolina dogs, Korean Jindo dogs and New Guinea singing dogs.
Their genetic profiles will expand a comprehensive DNA database the researchers are developing for a broad cross section of registered dog breeds. Armed with such information, the scientists hope to develop tests to screen dogs for genetic tendencies for such ailments as epilepsy, abnormal hip development, heart disease, cataracts and cancer.
The researchers also hope, now that the human genome has been deciphered, to contribute to efforts to better understand the genetic makeup of humanity's best and oldest friend.
Niels Pedersen , a veterinary professor who directs both the Veterinary Genetics Lab and the Center for Companion Animal Health, said a primary goal of the research is to better enable breeders to raise healthy, long-living dogs. The studies are funded by more than $300,000 in grants from the American Kennel Club's Canine Health Foundation.
Although mongrels are generally more genetically diverse and have fewer inherited disorders, the popularity of pedigreed dogs is increasing. Approximately 40% to 60% of pet dogs are from registered breeds, Pedersen said.
"People like purebred dogs because of their uniformity in size, color, shape and behavior. They all have their favorites," he said. "We're going to continue to have black Labs and golden retrievers. Therefore, let's give breeders the tools to make them as healthy as possible."
Pedersen and five other researchers are comparing the genetic makeup of 21 registered dog breeds with that of the wild canines. The selected purebreds represent all seven groups recognized by the American Kennel Club -- sporting, hound, working, nonsporting, herding, toy and terrier.
DNA samples, taken by rubbing a swab inside the animal's mouth, are donated by dog owners. The researchers are working to collect at least 50 samples from unrelated dogs of each breed. From the samples, they will create a database that they and other scientists can use to investigate genetic disorders that afflict certain breeds.
At the same time, researchers and conservationists in various parts of the world have sent the team about 200 DNA samples from dingoes, wolves, Jindo dogs and other wild canines.
The UC Davis study is one of the most comprehensive of its kind, said Marcia Eggleston, the lab's associate director and one of the dog DNA researchers.
Eggleston said the Veterinary Genetics Lab is seeking to develop diagnostic panels of 300 or more genetic markers, called microsatellites, scattered at predictable intervals along every canine chromosome. By comparing genetic profiles for both healthy and afflicted dogs in the same families, the researchers may be able to identify the genes responsible for some of the diseases.
One question the researchers want to answer is whether humans, by selectively breeding dogs to create different varieties, have significantly shrunk the size of the dog's gene pool. Even if the gene pool of a certain breed has been greatly diminished, they ask, is the collective genetic diversity among all registered breeds still equal to that of ancient dogs?
"If all of the genetic diversity still exists, it will make it a lot easier to restore genetic vigor to troubled breeds," Pedersen said. "The answers to these questions may be found in ancient breeds. The question is, 'How much genetic diversity was there in dogs before pure breeds began about a century ago?'"
The studies could reveal clues to the ancestry of the dog as a species. Dogs first left the wilderness to live with humans anywhere from 14,000 to 80,000 years ago, becoming the first domestic animals, Pedersen said. Cats, by comparison, became human companions about 4,000 years ago.
What those first dogs looked like is unclear. "It's still very much in debate whether dogs are closely related to wolves," said researcher Alison Schaffer.
Pedersen added: "There are significant genetic differences between the two, and it is more likely that dogs evolved from a definite species or subspecies of wolves.
"With time, this ancestral species became so closely intertwined with man -- and altered as companion, guard, worker of the flock and herd, hunter, etc. -- that it ceased to exist as a distinct species," he said. "However, it is still present collectively among the totality of what we now call Canis familiaris. You may get some insight into how this ancestral dog looked when you study dogs that have been allowed to breed freely for a number of generations and become feral, or in wild breeds like the dingo."
Dogs, when left to interbreed on their own, revert to a stereotypic form within a few generations -- stocky animals with yellowish, medium coats, curly tails, short muzzles and small, upright ears.
The researchers say genetic diagnostic tests they are working to develop could help breeders improve the quality of their dogs' lives. Some breeds are particularly afflicted by certain diseases. For instance, about 16 percent of Belgian Tervurens, an uncommon breed of herding dog, suffer from epilepsy. "If you try to completely eliminate this disease in this type of dog, you may eliminate the traits that you like in this breed," researcher Schaffer said.
The objective of good breeding is not necessarily to eliminate bad genes, but rather to manage pedigrees to minimize disease in the offspring, the researchers said.
Genetic screening tests would enable breeders to identify which of their dogs are carriers. By breeding those dogs to mates without the same gene, they could produce pups that might be carriers, but free of the disease. If the gene pool within a breed is too narrow, this approach may not work. Therefore, some breeds may have to crossed with other pedigrees periodically to improve the lines' health without sacrificing their distinctive traits, Schaffer said.
"Nobody deliberately wants to create a dog that's unhealthy," Schaffer said. "Breeders and pet owners all have the same ultimate goal, healthy happy companions."
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