Dogs were first domesticated by humans more than 14,000 years ago, and yet the extraordinary diversity of the more than 400 distinct canine breeds appears to have arisen through selective breeding within the past few centuries. The dog’s genome is thus a source of considerable fascination for geneticists.
In a study published last month in the Proceedings of the National Academy of Science, a research team sought “to map canine genome regions that show signs of recent selection and that contain genes that are prime candidates for further investigation. Those genes are being examined for their possible roles in the most conspicuous variations among dog breeds: size, coat color and texture, behavior, physiology, and skeleton structure.
“The researchers performed the largest genome-wide scan to date for targets of selection in purebred dogs. The genomes came from 275 unrelated dogs representing 10 breeds that were very unlike each other. The breeds were: Beagle, Border Collie, Brittany, Dachshund, German Shepherd, Greyhound, Jack Russell Terrier, Labrador Retriever, Shar-Pei, and Standard Poodle.”
Altogether, “the researchers catalogued more than 21,000 tiny variations in the genome. In investigating the relationships among the 10 breeds, they found that, genetically, 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.”
The 155 regions of the dog genome that appear to have been influenced by selective breeding contain 1,630 known or predicted protein-coding genes.
“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.
“A gene associated with dwarfism in mice, the study reports, appears to mediate variations in dog breed size and weight. Small-size breeds, like Dachshund, Beagle, Jack Russell Terrier, and Brittany have enormous differentiation in this gene, compared to larger-size breeds. Another region of peak differentiation in the dog genome, in an area thought to regulate muscle cell formation in embryos, seems to separate the German Shepherd, Jack Russell Terrier, Border Collie and Greyhound from the Dachshund, Beagle, Brittany, and Shar-Pei.”
For further details, see Dog Genome Researchers Track Paw Prints of Selective Breeding in EurekAlert! or this item at Science Daily.