Barcoded library preparation strategy. Forward and reverse PCR primers were designed with a unique ~10 nt barcode along with a ~20 nt site specific sequence, which will amplify around the CRISPR-Cas9 targeted site. In the first PCR cycle, either the forward or reverse barcode is added to end of the PCR product. In the second PCR cycle, the opposite barcode is added to each PCR product. In each subsequent cycle, both the forward and reverse barcodes are amplified along with the targeted region. After the PCR, sequencing platform specific adaptors are ligated to the pool of barcoded amplicons in a single reaction.