On the causes of evolutionary transition:transversion bias

Arlin Stoltzfus; Ryan W. Norris

How do these two relate to each other? The U matrix illustrates this relationship, because values of U scale with evolutionary rates, and U B has a known power as a conservative-radical distinction, namely AUC = 0.64. The ratio of U values for conservative replacements relative to radical ones is 2.7. That is, conservative . CC-BY 4.0 International license is made available under a The copyright holder for this preprint (which was not peer-reviewed) is the author/funder. It . https://doi.org/10.1101/027722 doi: bioRxiv preprint replacements as defined by U B are 2.7-fold more likely to be accepted in evolution than radical ones. This pair of values, AUC = 0.64 and evolutionary bias = 2.7, represents one point in the relationship between evolutionary acceptability and classification power for mutant fitness effects. There is another point where AUC = 0.5 (no power) and evolutionary bias = 1 (no effect). We can fill in the relationship further by randomizing U B , as shown in Figure 3 . The results show that, when about 75 % of the values are randomized, U B has an AUC of 0.53, equal to that of the transition:transversion distinction. This corresponds to an evolutionary bias of 1.3. The confidence interval of AUC from 0.50 to 0.56 for the transition:transversion distinction corresponds to the interval of 1.0 to 1.6 in evolutionary bias. That is, the expected evolutionary effect of the transition:transverion bias is a 1.3-fold bias, with a confidence interval from 1.0 (no effect) to 1.6. This makes it unlikely that selection plays the major role in causing the evolutionary transition:transversion bias, which typically is several-fold favoring transitions.