Though a toy breed, the Yorkie still retains much of its terrier ancestry in terms of personality. Individual dogs sometimes differ, but they are generally intelligent, independent and gutsy. Yorkshire Terriers are quick to determine where they fit in a household's "pack." Their behavior towards outsiders will vary - they often will be inclined to bark at strangers, but some Yorkies are outgoing and friendly towards new people while others are withdrawn and aloof. The differences in behavior in this regard are largely based on how the owner trains or conditions (and socializes) the Yorkie. A few individual Yorkshire Terriers may be timid or nervous, rather than bold, but the vast majority do seem to meet the breed standard for a confident, vigorous and self-important personality. Yorkies have great drive and stick-to-it-ive-ness, which are important hunting attributes. By the same token, they can be willful and stubborn.In a multi-breed home, the Yorkie will usually be the top "alpha" dog. However, bold does not equal aggressive. Yorkies typically get along well with other dogs and love to play together with them. Rather, bold character comes from the Yorkie's mix of great inquisitiveness, or an instinct to protect, and self-confidence. Some Yorkies are unaware of their small size and may even challenge larger, tougher dogs. Like many toy dogs, Yorkshire Terriers are active and quick. Yorkshire Terriers, as a breed, are intelligent dogs.
Yorkshire Terriers are a long-haired breed with no undercoat, which means that they do not shed. Rather, their hair is like human hair in that it grows continuously and falls out rarely (only when brushed or broken). This makes Yorkies one of the best breeds for allergy sufferers. Additionally, since Yorkies carry less dander on their coat, they generally do not have the unpleasant "wet dog" odor when wet. Yorkie puppies are born with a silky-soft black and tan coat and normally have black hairs mixed in with the tan until they are matured.The breed standard dictates that a Yorkshire Terrier must weigh no more than seven pounds.
Information from wikipedia.com