Graphic analysis of TAP and RAP . A schematic representation of AT skews at the third position of codon, A3/(A3+T3), plotted against GC skews at the third position of codon, G3/(G3+C3), for all CDS in a genome. The circles represent those CDS on the lagging strands (usually smaller numbers) and the leading strand (usually larger numbers). Line B
connecting the average points, (x2, y2) and (x1, y1), of these two populations represents the average distance between the populations. (A) Scenario I – presence of RAP only (no TAP). No TAP is present. RAP creates G and T excess in the leading strand (and A and T excess in the lagging strands), thus separating the two populations in the indicated direction. The relative strength of RAP corresponds to the length of line . Line B
(double arrows) intercepts the midpoint (0.5, 0.5). (B) Scenario II – presence of both RAP and TAP. TAP exerts asymmetric effect on CDSs on both the leading and lagging strands, thus pushing B
away from the midpoint (0.5, 0.5). The relative strength of TAP corresponds to B
(arrow), the distance between B
and the midpoint. Modified from Lobry and Sueoka .