Fig. 4. perd and Grip interact specifically in a novel RNAi interaction assay. (A) Injection of Grip dsRNA at high concentration phenocopies a loss-of-function mutation. (B-D) Representative embryos injected with perd dsRNA (B) or Grip dsRNA (C) at concentrations titrated to give minimal effect, and the stronger effect observed when they are combined (D). (E) Quantification of pooled data from four independent experiments, comparing the frequency with which effects are seen from each dsRNA individually or from both together, along with the distribution predicted if effects were additive (see Materials and methods for details). n=the number of informative embryos scored for each condition. The probability of obtaining the observed frequencies from the additive distribution was <10^-12 (² test). (F,G) In identical experiments, mib2 dsRNA does not exhibit synergy with perd or Grip dsRNA, despite causing detachment and rounding of a similar subset of muscles when injected at high concentration.