Distribution of read coverage depth for (a) Bv-95nt reads and (b) Phix-95nt reads. Read coverage was computed per base. In three separate calculations we considered all positions (black), positions in regions below (red) and positions in regions above (blue) the average GC content (%GC) of the reference. The regional %GC was determined based on a window of 250 bases upstream and 250 bases downstream of each position. In contrast to PhiX (b) the coverage variation in the sugar beet sample (a) is related to the %GC.