eEx25 [C13G4(cosmid) + XDM23(phage)]. Animals with eEx25 are WT. Pick wild-type to maintain. Animals which have lost eEx25 are Twitchers and Sterile (occasionally produce young). This cosmid lacks the 3' end of the unc-22 gene while XDM23 lacks the 5' end of unc-22, but following injection an extrachromosomal array was formed that included at least one functional unc-22 gene.