Genome Sequence of the Pea Aphid Acyrthosiphon pisum
CpG ratios were calculated using RefSeq data for each insect species. For each sequence the observed (obs) CpG frequency and the expected (exp) CpG frequency were calculated. The expected CpG frequency was calculated based on the GC content of each sequence and the CpG ratio was calculated as obs/exp. The frequency of each CpG ratio was plotted against the observed/expected ratio. A bimodal distribution was observed for A. pisum and A. mellifera, both of which show DNA methylation within the coding sequence of genes ,. D. melanogaster and T. castaneum both show a unimodal distribution, and there is only limited evidence of methylation in both of these species. In addition A. pisum and A. mellifera have all the DNA methyltransferases while D. melanogaster only has Dnmt2 and T. castaneum has Dnmt1 and Dnmt2.