a) Using the same BXD lines and covariates as described in the Online Methods, a QTL scan was performed for the overall mutation rate of each line. The green dashed line indicates the genome-wide significance threshold using 1,000 permutations (Bonferroni-corrected alpha = 0.05/15). b)Using the same BXD lines and covariates as described in the Online Methods, QTL scans were performed for the rates and fractions of all mutation types other than C>A. Green and blue dashed lines indicate the genome-wide significance thresholds for the rate and fraction scans, respectively, using 1,000 permutations (Bonferroni-corrected alpha = 0.05/15).