Gene 1 mutant No functional Proteins protein Gene f perform same function Functional protein Gene 2 mutant Functional proteIn Saturation No functional screening protein Cells still produce functional may not protein, even with a mutation recover all Wildtype gene Mutated gene g enes No functional Protein plays a role in proteIn early embryonic development Development arrested Protein plays a role wing development No adult, effects on wing development cannot be observed
Saturation screening may not recover all genes
Overexpression (a) Haploid cell Gene produces correct amount of protein to give normal function Promoter mutations overproduce protein, producing a mutant phenotype
Overexpression
Suppressor mutations (b) Haploid cell Protein complex Gene 1 Normal function Gene 2 Mutant gene ene 1 × Missing function Gene 2 Mutant gene Gene 1 Normal function Gene 2 compensating mutation
Suppressor mutations
Synthetic lethals (c) Haploid cell Gene 1 Normal function Gene 2 Redundant genes Mutant gene Genet (Defective protein Normal function Gene 2 Gene 1 (Defective protein) No function mutant phenotype C)(Defective protein is synthetic lethal Gene 2
Synthetic lethals
Nonallelic noncomplementation (d) Diploid cell Homologous 国■ chromosomes Functional proteins Gene 1 Gene 2 Reduced functional protein but still normal phenotype Gene 1 Gene 2 Reduced concentration of subunits leads to further reduction of functional protein, producing mutant Gene 1 Gene 2 phenotype
Nonallelic noncomplementation