BIOLOGY The family tree of dogs and wolves
Canine genetics can provide insight into human diseases.
WASHINGTON (AP) -- The tail-wagging, stick-fetching family pooch may be more closely related to Lassie, Rin Tin Tin or even White Fang than its human companions think.
Although dogs have about 99 percent of their genes in common, a few very distinct genetic differences separate them into some 400 breeds known worldwide.
Comparing dog genes to those of wolves, researchers found that a group of ancient dog types split off first. Later, the majority of canines evolved into three other clusters of dog variants -- hunters, herders and guard dogs -- largely because of breeding programs developed over the last several hundred years.
The new study of purebred dogs says among those closest to their wild wolf ancestors are the Siberian husky, Chinese shar-pei and African Basenji.
"One of the most interesting questions still to understand ... is why did the wolf keep locked in its genome everything that was necessary to make a Pekingese to a Great Dane," said Elaine A. Ostrander of the Fred Hutchinson Cancer Research Center in Seattle.
Similarities to humans
Ostrander, a co-author of the study in Thursday's issue of the journal Science, said dogs share the human environment and diseases, so learning more about their genetic development also can shed light on human diseases.
Human families are too small and "it's often difficult to get samples from more than one or two generations, whereas dog families are huge ... and you can get DNA for two, three, four generations," she said. "That gives you enormous statistical power for understanding the genetics."
In the process, scientists learned some interesting things about dogs.
For example, at least two breeds long thought to be ancient, the Ibizan hound and Pharaoh hound, were found not to be so old after all. Because of their resemblance to dogs depicted on ancient Egyptian tombs, they had been considered among the oldest of breeds. However, their genes indicate they have been developed in more recent times, the researchers said.
And two separate breeds recognized by the American Kennel Club -- Belgian Tervuren and Belgian sheepdog -- turned out to be genetically identical.
According to co-author Leonid Kruglyak of the Howard Hughes Medical Center, the study also found that although dogs have much in common, the 1 percent of their genes that determine different breeds are genetically quite distinct.
"These differences are so distinct that we could just feed a dog's genetic pattern into the database, and the computer could match it to a breed," Kruglyak said.
That was surprising because most of the breeds were genetically isolated only in the 19th century, with the advent of breed clubs and breed standards, she said.
Two branches of the canine family tree were the earliest to diverge from the wolves, the study found.
One branch includes the Oriental breeds shar-pei, shiba inu, chow chow and akita; the other the seemingly diverse breeds of African Basenji, Siberian husky, Alaskan malamute, Afghan hound and Saluki.
In addition to these ancient dogs, three other groups were developed later, including canines for guarding, herding and hunting.
Of 85 breeds tested, only four failed to show consistent sets of genes in common. They were the perro de presa canario, German shorthaired pointer, Australian shepherd and chihuahua.
The study also showed six pairs of breeds with very similar genetics: Alaskan malamute and Siberian husky, Belgian sheepdog and Belgian Tervuren, collie and Shetland sheepdog, greyhound and whippet, Bernese mountain dog and Greater Swiss mountain dog, and bull mastiff and mastiff.
Diane Vasey, director of development for the American Kennel Club Canine Health Foundation, said the research will help people who own dogs of unknown origin determine their pet's lineage or heritage as well as help veterinarians deal with genetic disorders associated with certain breeds.
"Being able to utilize the new findings of molecular genetics greatly enhances our ability to ensure longer, happier lives for all dogs, whether mixes or breeds," said Patti Strand, an AKC board member. "Previous dog breeders could only have dreamed of the future this research makes possible."
Vasey and Strand were not part of the research team, though the AKC helped the researchers obtain DNA samples.