Genetic evaluation of CRISPR-Cas9 off-target effects from deleterious mutations on Drosophila male single X chromosome

Clustered regularly interspaced short palindromic repeats (CRISPR)-associated nuclease protein 9 (Cas9) is a powerful tool used for genome engineering, but concerns remain about off-target effects. Here we evaluate potential deleterious effects of CRISPR-Cas9 by combining sequence analysis and the genetics of the male X chromosome in a Drosophila model. Since males have only one X chromosome deleterious mutations on the X chromosome will manifest in reducing viability or result in visible phenotypes and thus provide sensitive readouts of off-target activity. Our data do not support large scale off-target effects in Drosophila. To optimize sgRNA selection, we incorporated off-target evaluation into the PlatinumCRISPr sgRNA selection tool for a broad range of organisms.