Provided are approaches to improving CRISPR-based DNA editing by performing the editing in cells in which pol Θ (“POLQ”) enzyme and/or its function is reduced. Approaches are provided that are applicable to Cas9 nuclease and Cas9 nickase CRISPR editing. Also provided are kits that can contain a polynucleotide encoding a Cas9 and an agent for use in inhibiting POLQ, and/or or an expression vector configured for expressing a mutation template for use in CRISPR chromosome editing and an agent for use in inhibiting POLQ.