Dog crossbreed

Historically, crosses between dogs of different types were more well accepted at a time when modern purebred breeds (based on the eugenics principles) did not yet exist.

[2] An example to be cited is the famous case of Lord Orford's Greyhounds, which were improved by adding courage through the crossing with Old English Bulldogs, achieving the desired result after six generations.

[4] In the 1980s, a rise in Nordic-style sled racing in Scandinavia, characterized by shorter distances than typically seen in North American sled racing, led to the development of the eurohound and greyster, crosses utilizing German shorthair pointers with Alaskan huskies and greyhounds, respectively.

Jon Mooallem, writing in The New York Times, commented, "Given the roughly 350 inherited disorders littering the dog genome, crossing two purebreds and expanding their gene pools can be 'a phenomenally good idea,' according to one canine geneticist—if it is done conscientiously.

Wally Conron, writing in Reader's Digest, comments on the popularity of crosses after his introduction of the Labradoodle: "Were breeders bothering to check their sires and bitches for heredity faults, or were they simply caught up in delivering to hungry customers the next status symbol?

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,[18] is one strategy breeders can use to decrease the incidences of genetic defects.

This advantage can be progressively diluted when two crossbreeds are bred in the attempt to create a breed, narrowing the gene pool.

[20] In general it is believed that crossbred dogs "have a far lower chance of exhibiting the disorders that are common with the parental breeds.

[23] A Swedish study reviewing over 200,000 dogs registered for a veterinary insurance company in 1995 and 1996 found morbidity to be higher in most pedigrees than mongrels; however several pedigree breeds had a lower morbidity these are in order of highest risk to lowest risk: Drever, Norwegian Buhund, Schillerstövare, Jämthund, Gråhund, Siberian Husky, Karelian Bear Dog, Smålandsstövare, Finnish Spitz, and Norbottenspets.

Prolapsed nictitating membrane gland is a condition more common in the Puggle and Jug than both of the parent breeds, which shows the complexity of genetics and provides evidence against the theory of hybrid vigour.