trait with a retro-gene coding for fibroblast growth factor 4 (fgf4). therefore, it seems unlikely that dogs and humans are achondroplastic for the same reasons. however, histological studies in some achondroplastic dog breeds have shown altered cell patterns in cartilage that are very similar to those observed in humans exhibiting achondroplasia. a similar form of achondroplasia was found in a litter of piglets from a phenotypically normal danish sow. the dwarfism was inherited dominant in the offspring from this litter. the piglets were born phenotypically normal, but became more and more symptomatic as they reached maturity. this involved a mutation of the protein collagen, type x, alpha 1, encoded by the col10a1 gene. in humans a similar mutation (g595e) has been associated with schmid metaphyseal chondrodysplasia (smcd), a relatively mild skeletal disorder that is also associated with dwarfism. the now-extinct ancon sheep was created by humans through the selective breeding of common domestic sheep with achondroplasia. the average-sized torso combined with the relatively smaller legs produced by achondroplasia was valued for making affected sheep less likely to escape without affecting the amount of wool or meat each sheep produced.