Problem
Pretend that tail length in dogs is controlled by a single locus. On average, the tail of a dog with the long-tail genotype (TTTT) is 24 cm long while the average tail length for dogs with the short-tail genotype (tttt) is 10cm. You breed several long-tailed males, each to short-tailed females and, when grown, the tail length of the puppies averages 13 cm. What type of mode action does this demonstrate?