1.	Identify the nonrecombinant progeny (two most-numerous phenotypes).
2.	Identify the double-crossover progeny (two least-numerous phenotypes).
3.	Compare the phenotype of double-crossover progeny with the phenotype of nonrecombinant progeny. They should be alike in two characteristics and differ in one.
4.	The characteristic that differs between the double crossover and the nonrecombinant progeny is encoded by the middle gene.