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Man's best friend shares most genes with humans
> Full genome sequence to be published today<font>

Carl T. Hall, Chronicle Science Writer

Thursday, December 8, 2005

Scientists are publishing today the complete DNA sequence that makes a dog a dog, and it turns out to be uncannily close to what makes a person a person.

Genome sequencers at Harvard University, MIT and their affiliated Whitehead Institute for Biomedical Research in Cambridge, Mass., led an international team of scientists through a unique landscape of doggie DNA.

About 2.4 billion chemical units of DNA define a species uniquely shaped by people ever since dogs left the wolf pack and joined our human ancestors at least 15,000 years ago. Accurately mapping the dog genome took about two years and $30 million. Canis familiaris is the latest species to have its genetic code mapped, following that of the rat, mouse, fruit fly and, most famously, the human.

A report on the work appears today in Nature, the British science journal.

Simultaneously, Cold Spring Harbor Laboratory on Long Island devoted the December issue of its journal "Genome Research," exclusively to canine studies, and produced a book, "The Dog and Its Genome," co-edited by the Whitehead Institute's Kerstin Lindblad-Toh, lead author of the genome study.

Researchers note that dogs share many of the same gene-related health conditions as humans, including cancer and obesity. They have about 19,300 genes, scientists estimate, all but a handful close copies of human genes. Although humans have half a billion more DNA units, or "base pairs," that's mostly because humans are thought to have more silent stretches of so-called junk DNA.

"It's basically the same gene set in dogs and humans," Lindblad-Toh said during a telephone interview this week.

Dogs attract keen research interest in part because of their astounding variety of sizes, physical forms, coat colors and, of course, behavioral traits. If some of these variations can be traced to genes, results may shed light on more subtle variability in other species, including humans.

The task is made more manageable because the same breeding programs that generated the 350 or so modern dog breeds also left precise records of line- ages going back many generations. These are tied in some cases to detailed medical records and observations by trainers and owners -- a treasure trove in the era of comparative genomics.

After hundreds of years of selective inbreeding, many of the most prized purebreds have a high risk of genetic maladies. Discovery of a narcolepsy gene in Dobermans, for instance, helped scientists understand what caused the human form of the sleep disorder.

"The dog is a good model for human disease," Lindblad-Toh said. "They are highly intelligent, social animals, and we interact with them in the same environment."

In veterinary medicine, one of the big tricks now will be to see what disease susceptibilities might be linked genetically to traits that help define a breed.

"There are genes that make a Dalmatian look like a Dalmatian, and that could be very similar to genes that make a disease," said Erika Werne, director of canine research and education at the American Kennel Club Canine Health Foundation in Raleigh, N.C. "If we can see what sort of susceptibility an individual (dog) has, then we may be able to tailor therapies to that individual animal."

The full dog genome sequence was based on DNA samples taken from a female boxer named Tasha, chosen for technical reasons as the best reference breed for widespread use. Ten other breeds were then surveyed for gene variants important as mapping tools, including the dog's great ancestor, the gray wolf, and coyote cousin.

Having all these data in hand may help other researchers sniff out such mysteries as why some dogs, even after extensive training, fail to make the grade as reliable companions for blind and disabled people.

One other canine mystery came nearer to being solved today in a study, also appearing in Nature, on the astounding cornering capacity of greyhounds.

Two researchers in the United Kingdom, James Usherwood and Alan Wilson, used high-speed video to analyze the speed and footfall timings of 40 greyhounds tearing around a track after a mechanical hare. Results showed the dogs derive their power from their hips and back muscles while weight support on banked turns shifts to the forelimbs.

A human track star has to slow down on a sharply banked turn to compensate for rising forces of centripetal acceleration. Greyhounds can attack a bend full-speed, tilting into a turn like a cyclist, because "the muscles that provide the power are mechanically divorced from the structures that support weight," the scientists found.

"When you watch them run, you're in awe," commented Helen Hamilton, a Fremont veterinarian and longtime greyhound fancier, who likened the dogs to "Ferrari engines on four legs."

Genetically hardwired to run pell-mell, the dogs seem to get despondent if forced to slow down. Still, the speedy gene set comes at the price of shattered bones and torn tendons, Hamilton said, injuries whose incidence jumps dramatically in an environment full of two-legged track hounds laying wagers.

E-mail Carl Hall at [email protected].