Effect of dilution on strength of RNA interference (RNAi) phenotype. The RNAi phenotype of each nonviable gene on chromosome III  was assessed following dilution with increasing amounts of bacteria expressing a nontargeting double-stranded (ds)RNA. The percentage of genes with phenotypes that are either identical to that observed when targeted alone (red) or weaker than when targeted alone (blue) is shown for each dilution. This was examined for three phenotypes: (a) all nonviable phenotypes, (b) complete sterility (no progeny), and (c) partial sterility (some progeny). (d) False negative rate (in percentage) of combinatorial RNAi at a given dilution. Data shown are representative of two independent experiments performed in the RNAi-hypersensitive rrf-3 background .