A sequence cassette that encodes the following sequence elements has been inserted into the endogenous hh locus: a T2A peptide - an FRT3 site - the QF2 driver - an FRT site - a second T2A peptide - an FRT3 site - the lexA::GAD driver - an FRT site - an SV40 termination signal - a loxP cassette containing a Disc\RFP^{DsRed.3xP3.cUa} marker. The presence of the T2A peptides (which promote ribosomal 'skipping') ensures that QF2 and lexA::GAD are translated independently of each other and any upstream coding sequence of the endogenous hh locus. The presence of the mutually incompatible FRT and FRT3 sites means that FLP recombinase can be used to excise one of the two driver sequences.