20 July 2000

New DNA Research on Pedigrees

This week Animal Aid launched a new campaign highlighting a predicted 10% annual rise in the number of animals used in research thanks to the rapidly accelerating use of genetic manipulation. Meanwhile, scientists at the University of California 's Veterinary Genetics Laboratory have announced a new study analyzing DNA samples from domestic dogs and their wild cousins from around the world. The aim of the study is to expand a comprehensive DNA database 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. Niels Pedersen, a veterinary professor who directs both the Veterinary Genetics Lab and the Center for Comparative Animal Health, said a primary goal of the research is to better enable breeders to raise healthy, long-living dogs. Although crossbred dogs are generally more genetically diverse and have fewer inherited disorders, the popularity of pedigree dogs is increasing. Approximately 40 percent to 60 percent of pet dogs are from registered breeds. "People like purebred dogs because of their uniformity in size, color, shape and behavior. They all have their favorites," said Pedersen. "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 sporting, hound, working, nonsporting, herding, toy and terrier groups. DNA samples, taken by rubbing a swab inside the animal's mouth, are donated by dog owners. The researchers plan 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. 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. Cats, by comparison, became human companions about 4,000 years ago. 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. The objective of good breeding cannot necessarily be to eliminate 'bad genes', but rather to minimize disease in the offspring. According to the researchers, 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 be crossed with other pedigrees periodically to improve the lines' health without sacrificing their distinctive traits. Nobody deliberately wants to create a dog that's unhealthy. Breeders and pet owners all have the same ultimate goal, healthy happy companions. Related Sites: The Animal Aid Campaign