UAS regulatory sequences drive expression of two different sgRNAs, both of which target common coding exons within the 5' half of the Sk1 gene without overlapping the start codon; this is designed to result in an indel (small insertion or deletion mutation) of the target gene in the presence of a source of Cas9. Designed for conditional CRISPR mutagenesis; a GAL4 driver can be used to express the sgRNAs and a UAS-Cas9 transgene in a tissue-specific manner, inducing mutagenesis only in the GAL4-expressing cells.