BRCA1 and breast cancer: Using CRISPR-Cas9, we mutagenized the Dynll1 and Asciz genes in the KB1P-G3 Brca1-/-p53-/- murine mammary tumour cell line20, and monitored locus-specific indels within cell populations by deconvolution of complex Sanger sequencing traces derived from Cas9 cleavage site-spanning PCR amplicons using the Tracking of Indels by Decomposition (TIDE) algorithm41 (Supplementary Fig. 5a).