20xUAS regulatory sequences are fused upstream of a flip-excision (FLEx) switch cassette in which two pairs of mutually incompatible FLP target sites (FRT and FRT14) flank the hid coding sequence (in sense orientation relative to the UAS sequences) followed by the a Tag:M(CD4-Unk)-tagged tdTomato coding sequence (in anti-sense orientation relative to UAS). In the absence of FLP recombinase, the hid coding sequence is expressed under the control of UAS, resulting in cell ablation in cells expressing a source of GAL4. In the presence of FLP recombinase, the cassette can be inverted and stably locked in the opposite orientation, preventing hid expression and thus stochastically rescuing cells in which the inversion has occurred, with the rescued cells being marked with Tag:M(CD4-Unk)-tagged tdTomato expressed under the control of UAS.