registries and internet registry businesses will register dogs as any breed the owner chooses with minimal or no documentation; some even allow the breeder or owner to make up a designer "breed name" for their pet. Some crossbred dogs, created by breeding two purebred dogs of different breeds, may have the advantage of heterosis, or crossbreed vigor. This advantage can be progressively diluted when two crossbreeds are bred in the attempt to create a breed, narrowing the gene pool. The best way to continue taking advantage of crossbreed vigor is from the breeding of dogs of purebred ancestry, as this vigor is typically seen only in the first generation cross of two purebred animals of separate breeds, thus taking advantage of genetic diversity. See also Crossbreed, for any animal Dog type List of dog crossbreeds Puppy mill Purebred dog References External links Much Ado About Poo at canismajor.com Dog breeding