Over the past 14,000 years, more than 400 dogs have been produced through continuous domestication. Each has a unique physique, fur color, and habits. In order to discover the genetic mutations that cause specific traits in dogs, in 2009 Akey et al. Analyzed the genomes of 275 domestic dogs in 10 breeds. Previous research has found genes that produce specific characteristics, such as the short legs of a dachshund. They analyzed a range of dog breeds to determine the effects of centuries of selective breeding on the entire dog genome. The authors scanned the genetic records of nearly 300 dogs, including beagles, border collies, jack russell dogs, sharpei dogs, and standard poodles, and determined how selective breeding affected the genomes of these animals. The authors found that 155 different genetic locations may have played a role in generating the characteristics of purebred dogs, and suggested that this information may provide clues to the genes that produce specific breed shapes. For example, this group of scientists suggested that different versions of the HAS2 gene might have brought Shar Pei its unique wrinkled or smooth outer skin. Compared to the study of dog appearance characteristics, there are fewer studies on physiological characteristics. In 2012, Chen et al. Classified and sequenced the olfactory receptor gene family of dogs and wolves, and found that due to domestication, reproductive isolation, the evolutionary direction of olfactory receptor genes in dogs and wolves are not the same, and the olfactory receptor gene sequences in rural dogs in China More conservative.