The pCATCHA plasmid is designed to result in Cas9-triggered chain ablation (CATCHA) of a genomically encoded Spyo\Cas9 sequence. It contains a guide RNA (gRNA) that targets a site within the Spyo\Cas9 DNA sequence, driven by the ubiquitously expressed snRNA:U6:96Ab promoter. This gRNA is flanked by homology arms that correspond to the Spyo\Cas9 sequence found next to the cleavage site specified by the gRNA. The plasmid is inert in a wild-type genome, but in the presence of genomically encoded Spyo\Cas9, the gRNA will guide Spyo\Cas9 protein to cleave the genomic locus from which Spyo\Cas9 is expressed. Repair of the cleaved genomic Spyo\Cas9 sequence by homology-directed repair (HDR) will convert the genomic locus to CATCHA sequence (the gRNA flanked by homology arms that match Spyo\Cas9 sequences next to the gRNA-specified cleavage site) and ablate Spyo\Cas9 function. Conversion in heterozygous offspring favours amplification of CATCHA in the Spyo\Cas9-carrying population, acting as a potential gene drive 'brake'.