Sequence assembly
The invention relates to assembly of sequence reads. The invention provides a method for identifying a mutation in a nucleic acid involving sequencing nucleic acid to generate a plurality of sequence reads. Reads are assembled to form a contig, which is aligned to a reference. Individual reads are aligned to the contig. Mutations are identified based on the alignments to the reference and to the contig.
1. A method for assembling sequence reads, the method comprising:
obtaining a sample comprising template nucleic acid;
sequencing the template nucleic acid to generate a plurality of sequence reads;
inputting a reference genome and said plurality of sequence reads into
a computer system comprising a processor coupled to a non-transitory memory to perform the steps of:
assembling a contig from at least some of the plurality of sequence reads;
identifying a plurality of contig:reference descriptions of mutations by aligning the contig to said reference genome;
identifying a plurality of read:contig descriptions by aligning each of the plurality of sequence reads to the contig; and
combining the contig:reference descriptions with the read:contig descriptions to produce read:reference descriptions to map positional information of mutations found in the individual reads relative to the reference.
2. The method of claim 1 , further comprising attaching barcode sequences to the template nucleic acid.
3. The method of claim 2 , further comprising assigning the reads to subsets based on the barcode sequences.
4. The method of claim 3 , wherein each subset is used in creating a unique contig for that subset.
5. The method of claim 1 , wherein sequencing the template nucleic acid comprises fragmenting the template nucleic acid, attaching the fragments to a surface of channels in a flow cell, and amplifying the attached fragments to create clusters, each cluster comprising a plurality of copies of the same template in one of the channels of the flow cell.
6. The method of claim 1 , wherein creating the contig comprises overlap consensus assembly.
7. The method of claim 1 , wherein creating the contig comprises searching a prefix tree for overlap between the reads.
8. The method of claim 1 , further comprising identifying a mutation based on the alignments to the contig and the reference sequence.
9. The method of claim 8 , wherein a plurality of mutations are identified.
10. The method of claim 9 , wherein a first mutation is within about 100 nucleotides of a second mutation.
11. The method of claim 10 , wherein the first mutation is a substitution and the second mutation is a deletion.
12. The method of claim 8 , wherein the mutation is a deletion at an end of a sequence read.
13. The method of claim 1 , wherein sequencing is sequencing-by-synthesis.
14. The method of claim 13 , wherein sequencing-by-synthesis is single molecule sequencing-by-synthesis.
15. The method of claim 1 , wherein aligning the contig to a reference sequence is performed using a first set of alignment parameters and aligning each of the plurality of sequence reads to the contig is performed using a second set of alignment parameters.
16. The method of claim 15 , wherein the first set of alignment parameters includes a first gap penalty and a first substitution penalty; the second set of alignment parameters includes a second gap penalty and a second substitution penalty; and the first gap penalty>the second gap penalty.