How To Adjust Bwa Mem To Allow For Longer Gaps In Contig Alignment
My first guess would be to adjust the gap extension parameter. But that one is already set to 1, the lowest integer. I now get multiple split alignment, that are relatively very close to each other and I would rather have more of a end to end alignment.
Algorithm options:
-t INT number of threads [1]
-k INT minimum seed length [19]
-w INT band width for banded alignment [100]
-d INT off-diagonal X-dropoff [100]
-r FLOAT look for internal seeds inside a seed longer than {-k} * FLOAT [1.5]
-c INT skip seeds with more than INT occurrences [10000]
-S skip mate rescue
-P skip pairing; mate rescue performed unless -S also in use
-A INT score for a sequence match [1]
-B INT penalty for a mismatch [4]
-O INT gap open penalty [6]
-E INT gap extension penalty; a gap of size k cost {-O} + {-E}*k [1]
-L INT penalty for clipping [5]
-U INT penalty for an unpaired read pair [17]
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2 answers
If you want to follow through on your idea about decreasing gap costs, you can do something like -A 2 -E 1. At least in recent versions of bwa -A (which scales options -TdBOELU unless overridden) scales all costs, while -E will overwrite the scaled value, essentially decreasing extension costs.
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Try to set -O to 20 and -E to 0
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