26    ◾    Bioinformatics

bases in a base position and to quickly detect if there is any poor quality associated with

any tile. A graph with a completely blue color indicates an overall good quality base call

from all tiles (Figure 1.17a).

The quality losses associated with the physical positions on the flow cell are of different

causes. A random low quality at different positions is usually due to a technical problem

with the run such as the flow cell overlapping (Figure 1.17b).

FIGURE 1.16  The last records of the FASTQ file “SRR030834.fastq”.

FIGURE 1.15  Good per base sequence quality (with no warning).