Figure 1

Effect of set size on information entropy. The probability density of entropy values at four sites of the Influenza A PB2 proteins is plotted for alignments of decreasing sequence count N (graph A: N = 250; graph B: N = 50; graph C: N = 20). For each graph, we constructed 200 random alignments of the required size from the PB2 master alignment. The entropy mean and standard deviation measured from these alignments were used to plot the normal probability distributions shown in this chart. The entropy values for different sites are well-separated in large sequence sets (plot A) while the likelihood of distinguishing medium-entropy sites from high- or low-entropy sites drops dramatically at low sequence counts (plot C). The sites were selected based on their equally-spaced entropy values.