Fig. 3

Signatures of normalised CpG content (CpG[o/e]) reveal the presence and absence of historical DNA methylation in hexapods. Graphs are frequency histograms of CpG[o/e] with the y-axis depicting the number of genes with the specific CpG[o/e] values given on the x-axis. a Analysis of gene bodies in the honeybee (Apis mellifera), which has an intact DNA methylation system, reveals a bimodal distribution. b In contrast, the same analysis in Drosophila melanogaster, which does not have an intact DNA methylation system, reveals a unimodal distribution. c Analysis of Holacanthella duospinosa transcripts reveals a similar unimodal distribution consistent with the absence of an intact DNA methylation system in this species. The mean of this distribution is similar to the mean obtained for 1 kb fragments of the genome (d) and is consistent with a slightly lower than expected CpG content in the DNA sequence of H. duospinosa