Thanks to human selection and breeding, the physical appearance of dogs varies tremendously. Using only physical attributes as a guide, it’s safe to say that most uninformed biologists would have a hard time believing that a Chihuahua and a great dane were from the same species, let alone that they were capable of producing viable offspring together. In order to facilitate such dynamic intraspecies diversity of canines, people have long used random genetic mutations to their advantage. One example is the selection for various forms of dwarfism. Breeds such as the dachshund, corgi and the Basset hound have been created through selective breeding of individuals with a genetic mutation of the FGF4 gene that when inherited from one of their parents, leads to the characteristic short legs of these breeds. While a mutation for dwarfism is an expected standard for some breeds, it can be particularly undesirable in others.
A prime example of an undesirable mutation (especially for working dogs) is a mutation in the COL11A2 gene that causes a generally mild disproportionate dwarfism in the Labrador retriever known as skeletal dysplasia 2 (SD2). Disproportionate dwarfism is characterized by one or more body parts being smaller in comparison to overall ...