Dwarfism refers to an individual that is abnormally small in stature, usually with abnormal body proportions. Chondrodysplasia is a common form of dwarfism. These dogs are born looking normal but the long bones of the limbs fail to lengthen. In some dog breeds, like Dachshunds and Bassets, this is normal. Chondrodysplasia is due to a recessive gene mutation. Should it occur in Aussies, it would not be correct and affected dogs should not be used for breeding.
Another gene has been found that causes a longer, lower body outline not quite as extreme as that seen in chondrodysplastic dogs. It is not presently known if this gene is found in Aussies. Should it be found to be in the breed, it would be one to breed away from.
A longer, lower stature might also be selected for by breeders over time if it were to become fashionable; the genetics underlying such a shift could be complex and difficult to breed out if they became too common. Australian Shepherd breeders should keep in mind that the standard says the breed should be slightly longer than tall. This is the most functional form for a collie-type dog that sometimes must work in rough terrain and over long distances. Other body forms, however attractive, are not correct for this breed.