U. WASHINGTON (US)—Researchers have identified 155 regions on the canine genome that appear to have been influenced by selective breeding.
While domestication of dogs began well over 14,000 years ago, diversity among breeds originated in the last few centuries through intense artificial selection and strict breeding for desired characteristics.
Joshua Akey, assistant professor of genome sciences at the University of Washington, is the lead author of the effort to map canine genome regions that show signs of recent selection and that contain genes that are prime candidates for further investigation.
The researchers performed the largest genome-wide scan to date for targets of selection in purebred dogs. Their results were published in the early edition of the Proceedings of the National Academy of Sciences.
The genomes came from 275 unrelated dogs representing 10 breeds that were very unlike each other: beagle, Border collie, Brittany spaniel, dachshund, German shepherd, greyhound, Jack Russell terrier, Labrador retriever, shar-pei, and standard poodle.
The study was conducted, the researchers say, because the canine genome, the product of centuries of strong selection, contains many important lessons about the genetic architecture of physical and behavioral variations and the mechanisms of rapid, short-term evolution.
More than 21,000 tiny variations in the genome were catalogued and researchers found that genetically, among the 10 breeds, the German shepherd, shar-pei, beagle, and greyhound were especially distinct.
Their list of most differentiated regions of the dog genome included five genes already linked to hallmark traits of certain breeds: one for small size, one for short limbs like those in dachshunds and other stubby-legged dogs, and three for coats.
In calculating the overlap of the signatures marking selection in the genome, the researchers found that approximately 66 percent occurred in only one or two breeds.
They noted it was likely that these genome regions contain genes that confer qualities that distinguish a breed, such as skin wrinkling in the shar-pei.
In contrast, signatures of selection found in five or more breeds tended to sort the dogs into classes, and include, for example, a gene that governs the miniature size of breeds in the toy group.
The researchers honed in on a particular genome region in the shar-pei. Many of these dogs have excessive wrinkles, but some are smooth. The degree of skin folding correlates with levels of certain molecules whose production may be governed by a gene in this region.
Rare mutations in this same gene also cause severe skin wrinkling in people. Tiny genetic variations in this gene seemed linked to whether a sharpie would be smooth or wrinkled.
Despite the many insights emerging from their data, there were several limitations to their study and in interpreting the findings, the researchers say. They pointed out that a pattern of variation that is unusual to the dog genome at large doesn’t prove that specific genome region is under selection.
“This research has shown that artificial selection in dogs has acted on many of the same genes as natural selection in humans, and that many of these genes are regulators of gene activity,” explains Irene Extant, who oversees evolution grants at the National Institute of General Medical Sciences at the National Institutes of Health.
“The statistical and computational approaches used in this study will be of great value in deciphering the organization of human genetic variation, and in identifying the genetic basis of human characteristics.”
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