P is the P-value associated with the nonparametric bootstrap test (see Methods) that genes have a different nucleotide frequency in a given mutation than in its complement as seen from the leading strand (i.e., A→G includes A→G_leading and G→A_lagging). (+/−) P < 0.05; (++/−−) P < 0.01.

(NS) Nonsignificant difference.

(+/++) Gain or (−/−−) loss in the top change (e.g., A→G in the A→G and T→C comparison).