SNP discovery versus alignment depth. Proportion of SNPs identified in the D. serrata EST database versus contig alignment depth, restricted to the dataset of 1,254 'double hit' high quality SNPs. The total number of contigs for each alignment depth class (number of ESTs/contig) is represented by the height of the column. The different shading patterns within a column indicate the number of SNP classes (e.g. 1–5 SNPs/contig). Most contigs were shallow in depth (4–8 ESTs/contig) and contained relatively few (1–5 SNPs) sequence variants per contig. Note that here alignment depth is not constant across all sites along the contig and instead denotes the total number of ESTs per contig.