(a) Genetic scheme used for P-element transposase-based deletions. The crosses place P insertions (triangles) marked with flanking visible marker mutations (m1− and m2−) in males together with a source of P transposase (tnpase), so that hybrid element insertions can occur in premeiotic germ cells. Deletion events accompanied by recombination of flanking visible markers are identified in crosses to females carrying appropriate tester chromosomes. Deletions are established in stocks with balancer chromosomes (Bal). Dom and m3− represent other convenient dominant and recessive markers, respectively. (b) Genetic scheme used for FLP-FRT–based deletions. Crosses place two FRT-bearing transposon insertions (triangles) in trans in the presence of heat shock–driven FLP recombinase (hs-FLP). Activation of FLP recombinase results in the generation of deletions that can be detected by PCR. Deletions are established in isogenized stocks with balancers (Bal). Genotypes for nontransposon stocks (A, B, C, and D stocks) are provided in Table 1. Dom, dominant visible marker mutation; iso, isogenized chromosome; Y, Y chromosome.