Fig. 2. Crossing scheme for isolating mutants defective in GFP-Staufen localisation. The asterisk indicates the mutagenised chromosome. The red X shows a mitotic recombination event between the two FRT sequences, which occurs after induction of FLP expression in response to heat-shock. ovo^D1 is a dominant female-sterile mutation that blocks oogenesis at early stages. Within a clonal ovary, the only germline cysts that develop to later stages are those that are homozygous for the mutagenised chromosome.