Two KDRT sites have been inserted into the endogenous GluRIA locus (one within the 5'UTR, the other in an intron downstream of the translation start site). The 3' KDRT site is followed by sequence encoding a QF2 driver. In the presence of KDR the GluRIA exons are excised to create a null allele and the QF2 driver is expressed under the control of endogenous GluRIA regulatory sequences.