In whippets, wild-type dogs are skinny. A mutation in the myostatin gene causes dogs to become more muscular. Dogs containing one copy of the mutant myostatin gene are medium-muscled; dogs in which both copies of the myostatin gene are mutant are highly-muscled. A dog breeder mates a wild-type skinny dog with a highly-muscled dog. He then self-crosses the resulting F1 progeny. What are the phenotypic ratios in the F2 progeny?