Most adoption sites require shelters and rescues to list dogs under one to two breeds to help people search for particular types of dogs. However, without DNA tests, the best any of us can do is guess based on looks, size, and behavior.
Experiments have been held in which experts on dogs - breeders, vets, trainers, animal control officers, and shelter employees – were asked to identify the major breeds of a number of mixed breed dogs. There were wide variations in the breeds named for any individual dog and almost all the identifications of experts were incorrectly identified compared to DNA tests, and even different DNA tests can have different results.
The truth is that in mixed breed dogs (and many supposed “purebred” dogs from puppy mills or backyard breeders), few have any one breed representing 50% or more of their DNA, and most don’t even have two breeds which together make up half. Most DNA tests on mixed breed dogs show combinations of at least three major breeds (25% or more) and most have at least five or six breeds showing as 12.5% or more of their DNA, as well as many other breeds in smaller amounts that aren’t even listed on most test results.
The oldest breeds and widely breed or popular breeds frequently show up in these mixes. For example, Chow is an ancient breed and although purebred Chows do have black tongues, most dogs with black tongues or black spots on their tongues will have little or no Chow show up in their DNA. Read The Truth About Blue Tongues
One of the most often wrongfully identified breed is the "pit bull." Try out your own identification skills, see if you can identify the breed in the following: which dog is the real "pit bull."