Length, GC content and selective constraint distributions in three classes of intergenic regions in T. parva. Distribution of length (A), GC content (B) and selective constraint (C) per class of intergenic region (IGR) are depicted by boxplots. The three IGR classes (5'-5', 3'-5', 3'-3') are named according to the orientation of the flanking genes. Each box (interquartile range, IQR) contains the sample's 25% to 75% range (quartiles Q1 to Q3, respectively), with the bottleneck placed at the sample median. Horizontal tick marks show the range of all elements within Q1-1.5*IQR and Q3+1.5*IQR. Open circles mark data points outside this range, which are considered outliers. The width of the bottleneck (i.e the length of the V-shaped notch) is an indication of the confidence of the median; a lack of overlap of the bottleneck between samples implies that the medians are significantly different at ~95% confidence level. Similar results are found in T. annulata (not shown).