My single-breed dog doesn't look like just one breed. How is that possible?

Even in single-breed dogs, it is ultimately several genetic trait results (and not necessarily their breed), that are responsible for appearance. While breeders tend to strive for consistency in several of these traits to match a breed standard, this in no way precludes the possibility of a surprising outcome in a single-breed dog. 

Additionally, dogs with a single-breed result can sometimes have a very small percentage of DNA (about 1-5%) that represents a separate breed. These very small portions are typically undetectable by DNA test, but can yield some surprising looks in an otherwise single-breed dog.