Doggie DNA unravelled
Sequencing the canine genome could pinpoint causes of human diseases
Margaret Munro, CanWest News Service
Published: Thursday, December 08, 2005
Dogs are not only man's best friend, they're a geneticist's dream.

The inbred creatures are a showcase for genes that shape everything from the mild-mannered personality of basset hounds to the diminutive stature of toy poodles, say scientists who have completed the sequence of the canine genome.

The genome, which they liken to the instruction book of dog biology, holds the genetic keys to the extraordinary physical and behavioral differences seen in the 400 breeds of dogs now romping round the planet. Perhaps even more important, they say, the genome should help pinpoint genes linked to a long list of diseases that afflict both dogs and people.

It's a "remarkable resource," Dr. Francis Collins, director of the National Human Genome Research Institute, said from a teleconference in Boston Wednesday where the genome was unveiled at a dog show featuring 3,000 pedigreed pooches.

Tasha, a purebred female boxer from the U.S., donated the DNA sample that was sequenced to reveal a genome made up of close to 2.4 billion biochemical letters. Embedded in the sequence are about 19,300 genes, which compares to more than 30,000 genes found in the human genome.

"Of the more than 5,500 mammals living today, dogs are arguably the most remarkable," says Eric Lander, director of the Broad Institute at Harvard University and the Massachusetts Institute of Technology, and a senior scientist on the $30-million US dog genome project.

The international team, which publishes its finding in the journals Nature and Genome Research today, also catalogued 2.5 million genetic differences across 11 other canines -- from rottweilers to beagles to grey wolves.

The massive genetic map and database, which has been posted on the web, is expected to be a boon for dog breeders, biologists and medical researchers.

By comparing the genes that set breeds apart, Lander and his colleagues say the genome should make it possible to find the genes that control the incredible diversity in dogs, be they Great Danes that grow to 60 kilograms or chihuahuas that top out at three.

It is also reawakening behavioural genetics, which is a highly controversial field in human biology but fair game in the dog world where specific behaviours are prized and bred for. The scientists say it should be possible to find the genes that make sheepdogs herd and pointers point.

But, they say it may be a harder to find genes that underlie dog's aggression, separation anxiety and tendency to hide under the bed during thunderstorms. "Breed-specific behaviours will be easier to tackle," said Dr. Elaine Ostrander, a dog lover and geneticist at the U.S. National Institutes of Health.

Grey wolves were domesticated thousands of years ago and have been transformed into about 400 distinct breeds of dogs though selective breeding.

While the aim is to pass desired traits like coat colour or long legs or temperament from one generation in the next, intense breeding over the past 200 years has seen many disease-causing genes passed along. This explains why purebred dogs are prone to a long list of genetic disorders, including heart disease, cancer, blindness, cataracts, epilepsy, hip dysplasia and deafness.

"Each pure breed is an inbred, isolated genetic population, with simplified genetic structures that can be linked to their physical traits," Hans Ellegren, an evolutionary biologist at Sweden's Uppsala University, notes in Nature. This makes dogs a "geneticist's dream model of human genetic disease," he says, noting that Doberman pinschers are prone to narcolepsy, which makes them dose off, and German shepherds are predisposed to kidney cancer.

The new genome is already proving valuable for studying the genetic underpinnings of diseases and disorders common to both dogs and humans, says Ostrander, whose team is using the dog genome to map the genes associated with canine and human cancers. Because dogs are so inbred it is much easier to spot disease-linked mutations than it is in humans.