It can be tricky deciding if a Yorkshire terrier, also commonly called Yorkie, is purebred or non-purebred Yorkie mix. To decide if a dog is purebred, a careful examination of its physical characteristics has to take place. Organizations like the American Kennel Club keep lists of what each breed of dog should look like if it is a purebred.
Check the color scheme. According to the American Kennel Club, Yorkie puppies should be born black and tan in color. The black and tan hair will intermingle until the dog matures. To show a Yorkie in a competition, they have to have a blue color that is a dark steel blue and not a silver-blue. The blue color also needs to be separate and not intermingled with fawn, bronzy or black fur. The tan hair should be darker at the roots and become lighter at the tips. No black hair should be intermingled with the tan hair, leaving a purebred Yorkie with distinct patches of color not with intertwined color schemes. If any other color scheme or calico like color scheme develops, the dog is probably a mutt.
Examine a Yorkie's head. The head should be small and flat on the top and the muzzle should be relatively short according to the American Kennel Club. The nose should be black and the eyes are considered to be medium sized. The ears should be V-shaped, erect not floppy, and not set too far apart. Also, check the teeth. If a dog has crooked, broken or just odd looking teeth, there is a chance they are an inbred dog or a mutt. If the head is round on top, the muzzle is long and other characteristics of the head do not match what was described above, it is probably a non-purebred Yorkie.
Measure and weight a Yorkie. Yorkies are a small dog and should weigh 5 to 7 pounds. They are disqualified from American Kennel Club showing events if they weigh more than 7 pounds. Their height is about 6 or 7 inches from ground to shoulder, and the height at the shoulder should be the same as the height at the rump. The body should be compact and well proportioned.
Check a Yorkie's coat. The hair on a Yorkie should be glossy, fine and silky in texture. The coat should be moderately long and the hair needs to be straight. If the hair is wavy, it is a non-purebred Yorkie. The hair on the muzzle should be very long, normally hiding the face a little bit. The hair on the head often gets so long that owners need to put a bow in it to hold it back from falling in food bowls and allowing for maximum visibility. If a Yorkie is not growing long and luxurious hair, it is probably not a purebred.