Natural and artificial selection were not expected to act on similar classes of genes

With more than 400 distinct breeds, dogs come in a wide range of shapes, sizes, fur-styles, and temperaments. The curly-haired toy poodle, small enough to sit in a teacup, barely looks or acts like the smooth-coated Great Dane tall enough to peer like a periscope out of a car's sunroof. Not so apparent are breed differences in how the dogs' bodies function and their susceptibility to various diseases. Although domestication of dogs began over 14,000 years ago, according to Dr. Joshua Akey, University of Washington (UW) assistant professor of genome sciences, the spectacular diversity among breeds is thought to have originated during the past few centuries through intense artificial selection of and strict breeding for desired characteristics.

Akey 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. 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.The study was conducted, the researchers said, 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.

The findings, the researchers said, "provide a detailed glimpse into the genetic legacy of centuries of breeding practices." The 155 regions of the genome that appear to have been influenced by selective breeding contain 1,630 known or predicted protein-coding genes. The researchers tried to obtain a broad overview of the molecular functions of these genes. The were surprised to discover that genes involved in immunity and defense were overrepresented in the 155 regions, a phenomenon also discovered in genome analysis of selection in natural populations. Natural and artificial selection were not expected to act on similar classes of genes, the researchers noted, but immune-related genes may be frequent targets of selection because of their critical role in defending against ever-changing infections.

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 Shar-Pei would be smooth or wrinkled, and a rare genetic mutation was found in the Shar-Pei but not in other dogs.