Yorkies do not have an undercoat, but have silky hair, much like a human. One of the greatest things about the breed is that Yorkies DO NOT SHED. Yorkies are indoor dogs, but do enjoy a romp in the yard or a walk around the neighborhood. Yorkies from well bred stock are generally hardy and healthy and live to be 12-16 years of age. The AKC (American Kennel Club) breed standard is 4 to 7 pounds, many people refer to those under 4 pounds as "teacup Yorkies or T-Cup Yorkshire Terriers". This term is not recognized by the AKC, but I know that you mean a smaller than average dog. I do have small ones on occasion. Yorkies take on life with a gusto few others can match. Yorkshire Terriers are almost too cute to be real!