Encouraging desirable traits and discouraging others, breeders sought to create their ideal appearance or behavior, or both, for dogs, and, additionally, to ensure that the dogs could consistently produce offspring with the same appearance or behavior. Some consider mixed breeds undesirable, but mixing breeds can lead to desirable results, especially in the hands of an expert breeder. On the other hand, inexperienced crossbreeders can produce disastrous results. For example, the offspring of an obsessive Border Collie and an energetic, destructive Terrier could be dogs whose behavior is so erratic as to make the dogs a liability.
The Cockapoo results from deliberate crossbreeding.
Mixed-breed dogs can be divided roughly into three types:
- Crossbred dogs, which are mixtures of two known breeds. Some crossbreeds have traits that make them popular enough to be frequently bred deliberately, such as the Cockapoo—a cross between a Poodle and a Cocker Spaniel—and the Labradoodle, which mixes a Labrador Retriever with a Poodle. A Miniature Schnauzer/Poodle crossbeeds is called a Schnoodle. Other crossbreeds occur when breeders are hoping to create new breeds or to add or reinforce characteristics from one breed into another breed. Most crossbreedings, however, occur accidentally.
- Mixes among more than two breeds, such as when a crossbred dog mates with a purebred dog or with another crossbreed. The term mongrel is sometimes used to distinguish these dogs from crossbreeds.
- The generic Canis familiaris, seen in feral or pariah dog populations, where mixed breeding has occurred over many generations. These dogs tend to be light brown and of medium height and weight. This "genetic average" might also represent the appearance of the modern dog's ancestor.
