Figure 7

Effect of the degeneracy levels of codehop primers on PCR results. Results from the 10 bilaterian genera in which both primers were "codehop" were considered here (they cannot be directly derived from Table 1 since, for some introns, not all primer pairs were "codehop"). The bars represent the total numbers of cases (species × primer pairs) displaying results 'P', 'I' 'A' or nulls, for three categories of introns, those in which no (0), one (1) or both (2) primers have a more than 6-fold degeneracy. Exact tests were performed from the 4 × 3 contingency table used to build the histogram, as well as from tables derived from it after pooling some columns (for instance nulls versus "A + I + P"): all were highly significant. The pie chart diagrams display the proportion of the four categories of results within each category of degeneracy; they illustrate the increase in the proportion of null loci when primer degeneracy increases.