One may wonder that if this is not an official, recognized breed, how can they exist?
The answer is that the Yorkshire Terrier, of course, is an accepted and recognized breed. Some breeders purposefully produce litters of puppies with the goal being that they will be smaller than the standard.
Falling below the standardized size still allows the pup to be classified and registered as a purebred.
These tiny dogs are produced by a person selecting undersized dogs, both dam and sire, for mating. Genes are not only passed down from parents.
With canines, traits and characteristics are generally passed down from 5 generations back, on both sides (dam and sire).
Therefore, not only are 2 dogs chosen that fall under the normal size....but bloodlines are checked to see if there are smaller than average sizes in past generations as well.
In most cases, a larger female will be paired with a male....therefore, a pairing may be of a 3 or 4 pound female with a 2 pound male. There is no guarantee as to the size of the newborns in the litter
, however with genetics checked, this will most likely result smaller than standard pups.