Mean SNP density, dN and dS by gene category. Graph showing the mean SNP density, dN, and dS for different categories of protein-coding gene in the wMel genome. Error bars represent the standard error of the mean. Pseudogenes, genes that are potentially inactivated in wAu, IS elements and other genes with multiple ambiguous matches are excluded. The transcriptional regulator gene WD0255 is excluded as its closest wAu sequence contains a frameshift and is more similar to WD0623. dN – number of non-synonymous SNPs per potential site. dS – number of synonymous SNPs per potential site.