The genetic makeup of the dog — in this case a boxer named Tasha — has been deciphered and should help identify genes that make both dogs and people vulnerable to cancers, heart disease, diabetes, epilepsy, blindness, deafness and even some psychiatric disorders, scientists said Wednesday.
The work is the first virtually complete decoding of the species and illuminates the blueprint that shapes everything from the smallest Chihuahua to the biggest Great Dane.
"Outside of a dog, a book is man's best friend. Inside of a dog, it's too dark to read," quipped Dr. Francis Collins, director of the National Human Genome Research Institute, crediting the late comic Groucho Marx. "We're here to unveil the book of the dog."
Collins and other researchers made their announcement at a Boston dog show. The research, overseen by the Broad Institute of Harvard and MIT, was published in Thursday's issue of the journal Nature.
The researchers used the DNA of a family pet whose owners wish to remain anonymous. The female boxer named Tasha was chosen from more than 100 candidates because her DNA looked especially amenable to identifying its 2.4 billion chemical building blocks. But it turned out that any dog would do, said Eric Lander, director of the Broad Institute.
"It is a historic occasion today for the relationship between humans and dogs," he said of the animal domesticated 30,000 years ago. "Dogs are prepared to teach us new tricks."
The results are more complete than those announced in 2003 for the DNA of a male poodle named Shadow. Scientists have also deciphered the DNA of mice, rats, chimps, chickens and of course humans, as well as many other organisms.
At the DNA level, two randomly chosen dogs differ only about as much as two randomly chosen people, yet the variation in appearance, size and behavior in dogs is "just mind-boggling," Lander said in an earlier interview.
"How is it within one narrow gene pool you can produce Chihuahuas and Great Danes?" he asked.
Much of the answer involves differences in turning gene activity on and off, he said, and further study could improve the understanding of that.
The new work also identified signposts along the canine DNA that will help spot genes that predispose dogs to certain diseases, some of which they share with humans.
In fact, it may be vastly easier to find disease genes in dogs than in people. Intensive breeding has left its mark in the dog genome so that finding DNA regions with disease genes "is like hitting the side of a barn," Lander said.
Such research should benefit dogs and their owners, said William Truesdale, a board member of the American Kennel Club's Canine Health Foundation, which put $2 million into the dog DNA project.
"We're trying to erase these genetic frailties" by screening dogs for disease genes prior to breeding, he said. That effort is in its infancy, but over time, many of these genes can be eliminated through breeding, he said.
And puppies can be tested to assure their owners that they won't get certain diseases, "like a Good Housekeeping seal," Truesdale said.
Dog DNA is already teaching several lessons about human DNA. For one thing, comparisons between DNA of dogs, humans and mice revealed elaborate controls on the activity of certain human genes active in early development, Lander said.
The three-way comparisons also showed that some genetic features found in humans but not mice aren't really unique to people, but also appear in dogs, he said. "The more species we look at, the more, frankly, we find that humans are not exceptional here," Lander said.
Researchers also estimated that dogs have 19,300 genes, almost all of them canine versions of genes found in people. Prior studies have indicated that people have about 3,000 more, but Lander said the dog analysis "is leading us to question whether those are in fact real human genes." Some proposed human genes, he said, are now "suspect" and may not be genes at all.