Evaluation of window cohabitation of DNA sequencing errors and lowest PHRED quality values

When analyzing sequencing reads, it is important to distinguish between putative correct and wrong bases. An open question is how a PHRED quality value is capable of identifying the miscalled bases and if there is a quality cutoff that allows mapping of most errors. Considering the fact that a low quality value does not necessarily indicate a miscalled position, we decided to investigate if window-based analyses of quality values might better predict errors. There are many reasons to look for a perfect window in DNA sequences, such as when using SAGE technique, looking for BLAST seeding and clustering sequences. Thus, we set out to find a quality cutoff value that would distinguish non-perfect windows from perfect ones. We produced and compared 846 reads of pUC18 with the published pUC consensus, by local alignment. We then generated a database containing all mismatches, insertions and gaps in order to map real perfect windows. An investigation was made to find the potential to predict perfect windows when all bases in the window show quality values over a given cutoff. We conclude that, in window-based applications, a PHRED quality value cutoff of 7 masks most of the errors without masking real correct windows. We suggest that the putative wrong bases be indicated in lower case, increasing the information on the sequence databases without increasing the size the files.

Public sphere and the sustainability of the bioinformatics promise

The literature about genomics and bioinformatics achievements in high-impact journals such as Nature and Science has raised disproportionate expectations amongst the general public about fast and revolutionary drugs and breakthroughs in biomedicine. However, the yield obtained by database mining activities has been modest, as reported in the February 2001 issues of these journals featuring the completion of human genome draft sequences by the Human Genome Project Consortium and the company Celera. I have compared changes in rethoric employed by molecular biologists in 2001 and in April 2003, when the final sequence was announced. The comparison suggests that researchers are concerned about the sustainability of society’s investment in this field, though not explicitly.