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To build BWA-SW index select the Tools ‣ Align to reference ‣ Build Index item in the main menu. The Build Index dialog will appears. Set the Align short reads method parameter to BWA-MEM.

The dialog looks as follows:

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There are the following parameters:

Reference sequence — DNA sequence to which short reads would be aligned to. This parameter is required.

Index file name — file to save index to. This parameter is required.

Index algorithm (-a) — Algorithm for constructing BWT index. Available options are:

It implements three different algorithms

    • is — designed for short reads up to ~200bp with low error rate (<3%). It does gapped global alignment w.r.t. reads, supports paired-end reads, and is one of the fastest short read alignment algorithms to date while also visiting suboptimal hits.
    • bwtsw — is designed for long reads with more errors. It performs heuristic Smith-Waterman-like alignment to find high-scoring local hits. Algorithm implemented in BWT-SW. On low-error short queries, BWA-SW. is slower and less accurate than the is algorithm, but on long reads, it is better.
    • div — does not work for long genomes.

Colorspace (–c) — the input is read in colorspace, colors are encoded as characters A/C/G/T (A=blue, C=green, G=orange, T=red).