dog breeds were created from earlier breeds and types of dogs through the same kind of selective breeding that is used to create designer dogs. The Toy Poodle was bred down in size from the larger Standard Poodle, most likely by crossing with various very small Bichon types, such as the Maltese and Havanese. Most of the modern breeds have ancestries that include various older dog types and breeds; see individual breed articles for details of the origin of each breed. Health of crossbred dogs depends on their being descended from healthy parents. Breeders who select their breeding stock for cost-effectiveness and who skip health testing for the same reason will not produce puppies that are as reliably healthy as those bred by more conscientious breeders. However, studies of longevity in dogs have found some advantage for crossbreeds compared to purebred dogs. In general it is believed that crossbred dogs "have a far lower chance of exhibiting the disorders that are common with the parental breeds. Their genetic health will be substantially higher." Genetic defects Crossbreeding that takes advantage of the increased chance that a recessive detrimental allele will only be inherited from one parent and therefore not expressed in the phenotype of the offspring, is one strategy breeders can use to decrease the incidences of genetic defects. Knowing the disease incidence in the breed, and the genetic history of the individual, is important. Registration and recognition Crossbreed dogs are not recognized by traditional breed registries, even if both parents are registered purebreds. Breed associations such as the American Kennel Club, the United Kennel Club and the Canadian Kennel Club do not recognize designer crosses as dog breeds. If crossbred dogs are bred together for some period of time, and their breeding is well documented, they may eventually be considered a new breed of dog by major kennel clubs (an example of a recent crossbreed becoming a breed recognised by all major kennel clubs is the Cesky Terrier). New breeds of dogs must have a breed club that will document the ancestry of any individual member of that breed from the original founding dogs of the breed; when the kennel club that the breed club wishes to join is satisfied that the dogs are pedigreed, they will accept and register the dogs of that breed. Each kennel club has individual rules about how to document a new breed. Some minor