Threshold determination for the classification of contigs as chimeric and non-chimeric in the non-barcoded assemby of BAC pool 2. X-axis: minimal fraction of reads contributed by a sole BAC to a contig. Y-axis (logarithmic): fraction of total length comprised by those contigs. For all 3 assemblies (unmasked, masked in regions with 20mer frequencies >72 and >36) an exponential relationship was observed for fractions from a sole BAC <0.96, followed by a steep decline in the range between 0.96 and 1.00. Therefore, contigs with fractions ≥0.96 were classified as non-chimeric, whereas those <0.96 were regarded as chimeric.