TY - JOUR T1 - Transition-Transversion Bias Is Not Universal: A Counter Example from Grasshopper Pseudogenes A1 - Keller, Irene A1 - Bensasson, Douda A1 - Nichols, Richard A Y1 - 2007/02/02 N2 -
Some mutations occur more frequently than others. We need to understand these biases if we are to interpret the differences that have accumulated between species and individuals. Applications include estimating the time since evolutionary lineages diverged and detecting the signature of natural selection in DNA sequences. However, mutational biases have been obscured because, since mutations arose, natural selection has eliminated some whilst allowing others to persist to the present. We therefore study mutations that have accumulated in regions of the genome that are free from selection in a grasshopper with a gigantic genome. All other animal studies using this approach find an excess of mutations between DNA bases having similar biochemical properties (transitions rather than transversions). This bias has been widely interpreted as a consequence of the fundamental biochemical basis of mutation. However, once we exclude mutations associated with DNA methylation, we find no evidence of a transition bias, unlike the few comparable animal studies that make the same correction. We propose that this result indicates previously unanticipated differences between species in the selection on or mutation of their DNA.