 Then, the aggregate rate ratio (transitions to transversions) is "R = (1 * κu) / (2 * u) = κ / 2".For instance, in yeast, "κ ~ 1.2", therefore the aggregate bias is "R = 1.2 / 2 = 0.6", whereas in E. coli, "κ ~ 4" so that "R ~ 2".In a variety of organisms, transition mutations occur several-fold more frequently than expected under uniformity.