Yorkies typically have smooth coat with silky and wavy hair. They have a variety of colors. Their traits and appearance may depend on which of the parents have the most dominant genes. What breeders would do in order to achieve consistency with the appearance and size is they will pick the puppies with the certain traits and breed them for generations.
Yorki Poo (or Yorkie Poo, Yorkipoo, or Yorkies) was derived from crossbreeding Yorkshire Terrier and the Toy Poodle breeds. Essentially, they were bred as a toy and companion dog. Yorkies have been very popular in the last 20 years, especially in the United States, where the breed originated. One of the reasons for their popularity is that they are hypoallergenic (although this has been proven to be false).