In a non-complementation screen, an ENU-induced male is crossed with a female carrying a mutant allele ("a") of the gene of interest (A). If the mutation is dominant, then it will be present in every generation. However, if the mutation is recessive or if the G1 progeny are non-viable, then a different strategy is used to identify the mutation. An ENU-treated male is crossed with a wild type female. From the pool of G1 individuals, a heterozygous male is crossed to a female carrying the mutant allele ("a"). If the G2 progeny are infertile or non-viable, they can be recovered again from the G1 male.