A 'CopyCat' sequence cassette composed of 1. a snRNA:U6:96Aa promoter driving expression of a gRNA that targets e, 2. a Avic\GFPEGFP.3xP3.cLa marker, 3. homology arms to y at both 5' and 3' ends, has been inserted into the endogenous e locus. Used as part of a gene drive system; when combined with a source of Cas9, the 'CopyCat' sequence cassette can copy itself onto the e locus on the opposing chromosome by homology-directed repair (using the e homology arms present at the 5' and 3' ends of the cassette).