Not all yorkie breeders that belong to the AKC belong to the YTCA, but all YTCA members belong to the AKC. The YTCA is the parent club of the AKC and tells the AKC what the standard is. I would want a breeder that belongs to the YTCA, and I believe it would be easier to find an ethical breeder by choosing from their list. They have a code of ethics and conduct as found on this page:
Yorkshire Terrier Club of America Code of Ethics