Figure 2.

(Color online) Forward genetic screening schemes. A. Dominant screening identifies a heterozygous mutation (m/+) that causes phenotypic changes. B. Recessive screening identifies a homozygous mutation (m/m) that causes phenotypic changes. Compared with dominant screening, recessive screening takes a larger number of generations to identify a mutation. C. Suppressor screening begins with the injection of ENU to the phenodeviants (m/m). The effect of the suppressor mutation on the phenotype was assessed using heterozygous mutant mice (m/+). D. Histogram of a pedigree with a strong dominant phenotype. The two peaks are mice heterozygous for the mutant gene (m/+; red bars) and mice without the mutant gene (+/+; blue bars). E. Histogram of a pedigree with a strong recessive phenotype. The two peaks are mice homozygous for the mutant gene (m/m; red bars) and mice without the mutant gene (+/+; blue bars). Heterozygous mice (m/+) are omitted from this histogram. F. Histogram of heterozygous mutant mice (m/+) with a suppressor mutation (sup/+; green bars) or without the mutation (red bars). G. Histogram of heterozygous mutant mice (m/+) with an enhancer mutation (en/+; purple bars) or without the mutation (red bars).