Reciprocal cross is the cross, with the phenotype of each sex reversed as compared with the original cross, to test the role of parental sex on inheritance pattern. Related Theory Forward genetics is the examination of the genetic cause of an altered or abnormal phenotype introduced by a chemical mutagenesis or mutation by irradiation (e.g. phenotype → genotype). In reverse genetics, a particular gene is altered and the phenotype is investigated (e.g., genotype → phenotype).