While there are different breeds of dogs with short legs, they all have something in common: a genetic disorder. Short-legged dogs suffer from varying types of genetic dwarfism, which stunts their growth in utero. In some cases, breeders have historically manipulated the dwarfism-causing extra gene, engineering dogs with certain traits to make them more effective workers. Those breeds remain short-legged to this day.
Some dog breeds are born with a type of achondroplasia, or dwarfism. Though the type of achondroplasia and its severity can vary, it frequently results in legs that are disproportionately short for the body. These short-legged dog breeds include pugs, shih tzus, Welsh corgis, Pekingese, bulldogs, beagles and Scottish terriers.
In some cases, breeders have manipulated the gene pool by selectively breeding dogs with dwarfism, taking advantage of the extra gene to produce dogs suitable for working. The dachshund, for example, has a long and flexible body with short legs, making him well-suited for crawling into burrows and flushing out pest animals. The basset hound is another example of an "engineered" dog -- he was bred with short legs to slow down his pace alongside hunters. Though dogs like these are not frequently used for those purposes anymore, years of selective breeding have effectively redefined the physiology of these breeds.
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