tokens: Although there were similarities among the mutational patterns derived from N-OH-AAF-treated rats ( e.g. , G : C -- > T : A transversion was the most common mutation in all mutation sets ) , there were significant differences in the patterns of basepair substitution and frameshift mutation between the liver and spleen lymphocyte lacI mutants ( P = 0.02 ) and between the spleen lymphocyte lacI and hprt mutants ( P = 0.04 ) .