Figure 2

Expected deviations in PR2 plots in coding sequences and small intergenic regions among co-oriented genes. (a) The null hypothesis: mutation and selection are symmetric with respect to the two DNA strands; (b) replication-induced mutation pressure is asymmetric; (c) transcription- or translation-associated mutation or selection pressures are asymmetric; (d) all forces in (b) and (c) combined are asymmetric.