Here is an interesting chart showing categories of dog breeds based on their genetic makeup. National Geographic (February 2012 Issue):
Analyzing the DNA of 85 dog breeds, scientists found that genetic similarities clustered them into four broad categories. The groupings reveal how breeders have recombined ancestral stock to create new breeds; a few still carry many wolflike genes. Researchers named the groups for a distinguishing trait in the breeds dominating the clusters, though not every dog necessarily shows that trait. The length of the colored bars in a breed’s genetic profile shows
how much of the dog’s DNA falls into each category.
Wolflike
With roots in Asia, Africa, and the Middle East, these breeds are genetically closest to wolves, suggesting they are the oldest domesticated breeds.
Herders
Familiar herding breeds such as the Shetland sheepdog are joined by breeds never known for herding: the greyhound, pug, and borzoi. This suggests those breeds either were used in the creation of classic herding dogs or descended from them.
Hunters
Most in this group were developed in recent centuries as hunting dogs. While the pharaoh hound and Ibizan hound are said to descend from dogs seen on ancient Egyptian tombs, their placement here suggests they are re-creations bred to resemble ancient breeds.
Mastifflike
The German shepherd’s appearance in this cluster, anchored by the mastiff, bulldog, and boxer, likely reflects its breeding as a military and police dog.