When choosing a pet, many people opt for purebred pedigree dogs. Though they come at a price, it is easier to predict the eventual size, temperament, and needs of a purebred dog breed than for a ‘mutt’. But as a new BBC documentary, “Pedigree Dogs Exposed”,1 shows, the cost of breeding purebred dogs is genetic as well as economic.
All dogs are descendants of a wolf-like ancestor. This ancestor had the genetic diversity that allowed people to breed dogs as different in size as the Chihuahua and the Great Dane. Other traits such as colour, temperament, and exercise needs are just as diverse among the breeds. This great variability is an example of just how much genetic variation is built into the various created animal kinds.2 Other breeds, as will be shown, are the result of downhill mutations.
Over many hundreds of years, humans have produced the various breeds by specifically selecting different traits to breed for; there are currently over 200 distinct varieties of dog, but all belong to the same species, and could theoretically breed with each other, though size difference between larger and smaller breeds renders some combinations unlikely.3
Over time, breeding only for certain traits allows great predictability in what a dog’s offspring will look like—a Dalmatian mated with a Dalmatian will produce Dalmatian puppies, and so on. When this occurs regularly, the type of dog becomes an official breed. But this predictability comes at a genetic cost. The breeders have drastically reduced the amount of genetic information in the population of dogs—such as for other coat colours and lengths, or different sizes or temperaments. This sort of selection is done on purpose, but there are other traits that are inadvertently selected for as well….
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