 In Kimura's original description of the model the α and β were used to denote the rates of these types of substitutions, but it is now more common to set the rate of transversions to 1 and use κ to denote the transition/transversion rate ratio (as is done below).The K80 model assumes that all of the bases are equally frequent (formula_96).Rate matrix formula_97 with columns corresponding to formula_98, formula_99, formula_100, and formula_101, respectively.