Removed instruction on ALT alignment
Favoring the new method
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README.md
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README.md
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@ -130,38 +130,6 @@ case, BWA-backtrack will flag the read as unmapped (0x4), but you will see
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position, CIGAR and all the tags. A similar issue may occur to BWA-SW alignment
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as well. BWA-MEM does not have this problem.
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####<a name="h38"></a>6. How to map sequences to GRCh38 with ALT contigs?
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BWA-backtrack and BWA-MEM partially support mapping to a reference containing
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ALT contigs that represent alternative alleles highly divergent from the
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reference genome.
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# download the K8 executable required by bwa-helper.js
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wget http://sourceforge.net/projects/lh3/files/k8/k8-0.2.1.tar.bz2/download
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tar -jxf k8-0.2.1.tar.bz2
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# download the ALT-to-GRCh38 alignment in the SAM format
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wget http://sourceforge.net/projects/bio-bwa/files/hs38.alt.sam.gz/download
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# download the GRCh38 sequences with ALT contigs
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wget ftp://ftp.ncbi.nlm.nih.gov/genbank/genomes/Eukaryotes/vertebrates_mammals/Homo_sapiens/GRCh38/seqs_for_alignment_pipelines/GCA_000001405.15_GRCh38_full_analysis_set.fna.gz
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# index and mapping
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bwa index -p hs38a GCA_000001405.15_GRCh38_full_analysis_set.fna.gz
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bwa mem -h50 hs38a reads.fq | ./k8-linux bwa-helper.js genalt hs38.alt.sam.gz > out.sam
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Here, option `-h50` asks bwa-mem to output multiple hits in the XA tag if the
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read has 50 or fewer hits. For each SAM line containing the XA tag,
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`bwa-helper.js genalt` decodes the alignments in the XA tag, groups hits lifted
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to the same chromosomal region, adjusts mapping quality and outputs all the
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hits overlapping the reported hit. A read may be mapped to both the primary
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assembly and one or more ALT contigs all with high mapping quality.
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Note that this procedure assumes reads are single-end and may miss hits to
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highly repetitive regions as these hits will not be reported with option
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`-h50`. `bwa-helper.js` is a prototype implementation not recommended for
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production uses.
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[1]: http://en.wikipedia.org/wiki/GNU_General_Public_License
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