Genetic scientists explore how centuries of breeding have altered dogs' DNA
Dog genes that code for such signature pet traits as the furrowed skin of the Shar-Pei have been identified in a study that shows how centuries of breeding gave rise to 400 kinds of domestic dogs.
Researchers analyzed the genes of 275 dogs in 10 breeds to see how breeding practices have altered their DNA, the hereditary template in their cells. The results, reported last week in the Proceedings of the National Academy of Sciences, show that some conspicuous physical traits, or phenotypes, such as height and coat color, can be traced to particular genes of beagles, border collies, dachshunds and poodles, among other breeds.
"When you have a Chihuahua that's nine inches tall and a Great Dane that is seven feet tall, that can be traced back to IGF1," the gene that influences dog size, said Joshua Akey, a geneticist at the University of Washington in Seattle who was the paper's lead author.
Understanding how breeding leads to artificial selection of some doggy DNA can clarify the way genes give rise to appearance and behavior in other species, the researchers said. Such knowledge "holds considerable promise for providing unique insights into the genetic basis of heritable variation in humans," they wrote.
Dogs are "a great system for understanding how genetic variation influences how individuals in a population act differently, look different and have different susceptibilities to disease," Akey said in a telephone interview.
Domesticated dogs have been bred for more than 14,000 years, the report said. The strict form of selective breeding used today to turn out desired characteristics in the animals is a more recent phenomenon.
"Most dog breeds were formed in the last 500 to 1,000 years, a relatively short time frame in terms of evolution," Akey said.
Today there are more than 400 genetically distinct breeds of domestic dog, yet "relatively little progress has been made on systematically identifying which regions of the canine genome have been influenced by selective breeding during the natural history of the dog," the study said.
To pursue this, the researchers analyzed the full set of genes, called the genome, of 10 breeds of domesticated dogs to locate the most-differentiated regions of their genes. Of the 10, the most genetically distinct breeds were the German shepherd, Shar-Pei, beagle and greyhound.
The researchers were able to zero in on one specific gene, called HAS2, which causes deep wrinkling in the skin of the Shar-Pei. The breed is characterized by a sandy coat, furrowed skin and a wide muzzle, according to the American Kennel Club, the nation's largest purebred dog registry. The HAS2 finding was confirmed in two follow-up analyses.
This gene is of particular interest, Akey said, because HAS2 mutations in humans can lead to a skin condition called cutaneous mucinosis. This rare disease affects mostly young people and involves skin lesions and inflammation, according to the American Academy of Dermatology.
Previous analyses of canine genomics had linked four genes to physical traits including coat color and texture, leg length and size. The researchers in this study were able to confirm all four earlier findings, including variations in the genes IGF1 and FGF5 that account for the differences in dogs' size and limb length, respectively.
Akey and his team also identified 150 new gene locations, containing more than 1,600 genes, that have been altered by artificial selection. They plan further testing of these genes, he said. The study was funded by the National Institutes of Health and the Alfred P. Sloan Foundation.
-- Bloomberg News