Method for accurate sequencing of DNA

A method of sequencing DNA using a sequencer, comprising:

• (a) generating a sequencing library comprising the steps—
• attaching sequencing adapters to a plurality of DNA fragments to form a plurality of adapter-DNA molecules;
• and
• amplifying the adapter-DNA molecules to generate clonal strands of each adapter-DNA molecule;
• (b) flowing a plurality of clonal strands over a sequencer flow cell such that multiple clonal strands of adapter-DNA molecules bind to the flow cell;
• (c) bridge amplifying the bound strands of adapter-DNA molecules to form one or more polonies;
• (d) sequencing the polonies to obtain a preliminary sequence read for each polony, wherein for each polony, sequencing includes—
• obtaining fluorescence intensity measurements for each nucleotide position of the polony;
• and
• performing a first round of base calling by converting the fluorescence intensity measurements into a probable base call for each nucleotide position of the polony to provide a preliminary sequence read, the preliminary sequence read having a preliminary error probability;
• (e) grouping preliminary sequence reads generated from the clonal strands derived from a particular adapter-DNA molecule;
• (f) calculating a fluorescence intensity measurement average for each nucleotide position from the grouped preliminary sequence reads;
• and
• (g) performing a second round of base calling for each nucleotide position of the grouped preliminary sequence reads -using the fluorescence intensity measurement averages to provide a sequence read;
• (h) wherein an error probability of the sequence read corresponding to the particular adapter-DNA molecule is lower than any one of the preliminary error probabilities of the individual preliminary sequence reads in the group.