The formation of the teacup dog is the result of a genetic mutation, where smaller dogs are bred and reproduced. After several generations of breeding in this way, the offspring retain the gene for smaller size, and thus the dominant gene causes the dog to be smaller in size. However, by keeping the gene that controls the smaller size, the singularity of the gene after several generations of breeding leads to a genetic mutation. This results in a teacup dog that is small, but has a recessive gene defect that often goes unnoticed. The common teacup Teddy and teacup Pomeranian on the market are the better breeds selected through genetic breeding. These two teacup dogs do not have the recessive genetic defect, only a relatively short life span.
