To test the clone tracking capacity of sgRNA-barcodes, we applied the 26-nt barcode library to monitor clonal resistance to the BET-bromodomain inhibitor JQ1, in D458, a MYC-amplified medulloblastoma cell line known to contain pre-existing resistant clones to BET-bromodomain targeting therapeutic agents (a chemotherapeutic) [5]. The gene discussed is DNER; the disease is medulloblastoma.