Good dog breeders, the ones who breed for health and temperament rather than quantity or money, never (outside of exceptional circumstances) breed a dog whose genetic background they donu2019t know. Some countries, such as Finland for example, have online databases of family trees for a given breed. The Finnish database lists any official test results for a given dog, which pairing resulted in an epileptic puppy and should therefore not be bred from again, cause of death for any dog whose death has been reported, and other pertinent facts like show performance and disqualifying illnesses.All this means that good breeders will (with very few exceptions) only use dogs from recorded lines, not some random dog that looks kinda like [insert breed here]. Registered (read: purebred) dogs are all microchipped, and the chip numbers are added to the database when the breeder registers a litter.If a dog of unknown origin (looks like [insert breed here] but has no papers) has some incredible quality that they really want to breed in and a temperament to match, they might decide to do genetic testing. Theyu2019ll also get a vet to do official tests on the dogu2019s hips, knees, eyes, heart - anything that might have structural problems that could be passed on to the next generation.Then, and only then, will they (maybe) breed this dog of unknown parentage.If there isnu2019t an incredible quality, they simply wonu2019t take the risk of breeding that dog.