Expression levels and piRNA coverage around genes. Genes are divided according to their expression levels in adult testis (high/medium/low) as indicated below charts. The median piRNA coverage of RTEs around genes are shown as rectangles with error bars denoting 25 and 75 percentiles. Coverage values are normalised by the number of base pairs occupied by RTEs around the genes. Using a Mann-Whitney U test, all values for highly expressed genes are significantly higher than the corresponding values for lowly expressed genes for all four RTE types. Significance levels shown in Additional File 1, Table S3.