These motifs focus on known trouble spots. Because GC base composition is frequently implicated in coverage bias, it is also useful to measure the relative coverage across the entire GC spectrum by grouping all 100-base sliding windows across the genome by their GC content and reporting the average relative coverage for each GC-content percentage (in effect defining a motif for each percentage). The results can be presented as a GC-bias plot, as exemplified in Figure 2. Unbiased sequencing would be unaffected by GC composition, resulting in a flat line along relative coverage = 1.
