Breed Fragmentation. In addition to the founders effect selective breeding has on the gene pool when a breed is created, Breed Fragmentation can restrict the gene pool even further. In some cases, fanciers choose to further reduce the gene pool for the sake of creating even more distinctions within a breed. For example, a breed might have both long-haired and short-haired dogs, but some fancier decides that they want to create a distinct 'type' within the breed; perhaps a purely long-haired variety. Instead of breeding the long-haired and short-haired dogs together, the fancier only breeds long-haired dogs to other long-haired dogs, further shrinking the gene pool. This is called breed fragmentation. Breed fragmentation creates unnecessary inbreeding within a breed. In purebred dogs, dogs remain purebred as long as they're crossed with other purebred dogs of the same breed. The gene pool is relatively small but consists of all other dogs in their breed. Breed fragmentation further limits the gene pool by restricting breeding to a small number of individuals within the already restricted gene pool. For example, a hypothetical gene pool for a rare breed may contain 700 purebred dogs of breeding age. However, a breed fancier wants to ensure that his dogs have longer fur, so he limits his breeding program only to other members of the gene pool who have the longest fur. This may only be 100 individuals out of the 700 available possibilities within the breed. Restricting his breeding to those 100 individuals is breed fragmentation. If a breed standard accepts both long-haired and short-haired varieties, then there's no reason that these varieties can't be bred together. They'd still conform to the breed standard and still be able to be registered as purebreds. Instead, however, fanciers make arbitrary distinctions that further narrow the gene pool unnecessarily. The Norwich and Norfolk Terriers, for example, started as one breed. At one point, fanciers decided that they wanted to breed based on the dog’s ears; dogs with prick ears (ears that stand up) were bred to other dogs with prick ears. Dogs with drop ears (ears that droop or fold down over the dog's head) were bred with other like dogs. There was no interbreeding between the two ear types, even though they were the same breed, simply because fanciers wanted to change the shape of the dog's ears. Breed fragmentation also occurs because breeders separate dogs into 'working' types and 'show' types, and breed for those characteristics. 'Show' dogs might be bred for their confirmation with the breed's physical description, including color, body characteristics, and gait. 'Working' dogs might be bred for temperament and the ability to perform certain tasks. Breeders who make this arbitrary distinction don't interbreed the two types, even though they're all the same breed, thus further limiting the gene pool and contributing to breed fragmentation.