DNA analysis of dogs produces surprises

Look at 85 breeds reveals some unexpected history, could help human health

May 21, 2004|By Michael Stroh | Michael Stroh,SUN STAFF

Scientists have completed the most sweeping genetic analysis of purebred dogs ever and, while it could lead to new DNA tests and disease cures, what's likely to set tails wagging is this: Some pooches, it seems, have a few unexpected skeletons in the family doghouse.

German shepherd owners, for example, might admire the breed's lupine good looks. But it turns out the weirdly wrinkled Chinese shar-pei is actually more wolfish, at least when it comes to its DNA.

Then there are Ibizan and pharaoh hounds, whose likenesses adorn the walls of Egyptian tombs. While some owners brag that their animals have the most ancient bloodline of any breed, DNA tells a different tale: The hounds were concocted by mating more modern dogs.

"I think there's some people in the breed that could be disappointed," says Heidi Clevenstine, president of the Ibizan Hound Club of the United States.

In the new study, published today in the journal Science, Elaine Ostrander of the Fred Hutchinson Cancer Research Center in Seattle and her team analyzed DNA of more than 400 domestic purebreds from 85 breeds, from tiny Chihuahua to super-sized Saint Bernard.

Besides uncovering tantalizing clues about the evolution of various breeds, the researchers also discovered each breed carried its own distinct genetic signature. Scientists said this finding could pave the way for a simple genetic test to untangle a mutt's mixed ancestry. The test could also help breeders reassure prospective buyers that an animal's pedigree is pure.

"Long-range, I can envision when every dog who comes into a shelter has a DNA test done on it," said Robert Kelly, a member of the board of directors of the American Kennel Club Canine Health Foundation, which helped fund the study.

The study's lead author, Leonid Kruglyak at the Hutchinson Center, said he was startled by the genetic variation among breeds - a difference even greater than "among human populations that evolved on different continents."

The reason, scientists said, is that dogs are probably the most genetically manipulated mammals on Earth. Recent DNA studies show Canis familiaris diverged from East Asian wolves roughly 15,000 years ago and then trailed humans overland to Europe and across the Bering Strait to North America. As early dog populations became isolated from one another, distinct breeds began to emerge, scientists say.

But the process accelerated in the 19th century with the rise of European breed clubs, whose strict mating rules and meticulous records helped ensure that bloodlines remained pure.

Today there are more than 400 breeds of dog, although fewer than half are recognized by the American Kennel Club.

To conduct the study, Ostrander and her colleagues traveled to dog shows and contacted breed clubs for DNA samples, scraped painlessly from the dogs' cheeks. Computers then helped spot tiny genetic variations in the samples. By analyzing these differences, Ostrander and her colleagues were able to show which breeds were ancient and which were modern.

The most ancient group, sporting the most genetic similarity to its wolf ancestors, included breeds as diverse as the shar-pei, Siberian husky, Lhasa apso, shiba inu and Pekingese.

Breeds of more recent vintage included the bulldog, Rottweiler, German shepherd and the Norwegian elkhound, despite lore that the latter dog's line goes back 5,000 years to Scandinavia.

Nailing down the genetic relationships between canine breeds could help scientists understand the molecular underpinnings of breed behavior or appearance, such as why border collies have a knack for herding or why poodles sport a curly coat.

More importantly, it could also help ferret out disease-causing canine genes, says Ostrander, who notes that the animals are susceptible to more than 350 inherited diseases.

But Ostrander, whose lab studies human prostate and breast cancer, stresses it's not just dogs that could benefit from her study. Because the DNA of canines and their human companions is similar, scientists increasingly turn to dogs for help in understanding diseases from cancer to epilepsy.

In coming weeks, efforts to find shared disease genes could get a boost when scientists at the Broad Institute in Cambridge, Mass., unveil the first detailed map of canine DNA.

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