Number of (A) Arabidopsis thaliana and (B) Oryza sativa probe-pairs and probe-sets used to study the transcriptome of A. thaliana and O. sativa respectively, as a function of the gDNA hybridisation intensity thresholds used to generate the probe-mask files. Filled circles are scaled to the left-hand y-axis (i.e. probe-sets retained within probe-mask files) and unfilled circles are scaled to the right-hand y-axis (i.e. probe-pairs retained within probe-mask files). Three gDNA hybridisations were performed for each species.