Using the strand-assignment patterns of clustered mutations arising from these ssDNA sources in yeast, we then scrutinized over 10,000 mutation clusters in cancers with a high level of APOBEC mutagenesis and found that clusters in cancers matched patterns of clustered mutations in resection-defective yeast, suggesting that bidirectional resection does not play a major role in cluster formation, but rather, clusters in cancer are formed by a BIR-like mechanism. This evidence concerns the gene KCNJ11 and cancer.