This is called inbreeding and should NEVER be done, IMO. Like others have mentioned, if there are any undesired traits in the genetic background, this type of breeding promotes those traits to present themselves. I can't even pretend to understand the knowledge and experience needed for breeders to test breed some dogs. As you said, this was an accident
, not something you intentionally let happen, but I really hope there are NOT people out there making this type of breeding a routine practice just at the hope to produce smaller dogs.
