Question: When Hard clipping is used instead of the Soft clipping ?
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gravatar for 2012secondseason
8 weeks ago by
2012secondseason10 wrote:

Hi all. The documentation for Samtools is minimal at best. I'm still confused on the concept of a clipped read.

I know that there are many explanations here that soft clipped bases are present in SEQ unlike hard clipped bases. But it's insufficient. In what cases, use H instead of S ??

Thanks.

hard clipping cigar clipping • 168 views
ADD COMMENTlink modified 8 weeks ago by Devon Ryan81k • written 8 weeks ago by 2012secondseason10
3
gravatar for Pierre Lindenbaum
8 weeks ago by
France/Nantes/Institut du Thorax - INSERM UMR1087
Pierre Lindenbaum108k wrote:

in bwa, HARD clipping is used for supplementary reads.

Information (full read sequence) is still available in the primary alignment.

ADD COMMENTlink written 8 weeks ago by Pierre Lindenbaum108k
3
gravatar for Devon Ryan
8 weeks ago by
Devon Ryan81k
Freiburg, Germany
Devon Ryan81k wrote:

This is purely up to the program creating the file, which is why this isn't described in the samtools documentation. A good example of a time when most programs would hard-clip a read is if they remove known adapter sequence. It's then not worthwhile including that sequence in the output. One could also think of hard-clipping regions when they're part of supplemental alignments (I've seen both hard and soft-clipping for that, though the former is probably more useful).

ADD COMMENTlink written 8 weeks ago by Devon Ryan81k
2

2012secondseason, for example, BWA mem gives you some control how you'd like to have the clipped sequences represented - you can toggle between soft and hard clipping using the -Y option. There used to be an option to remove soft clipping altogether, but that seems to have changed its meaning (at least comparing the online manual to the command line description)

ADD REPLYlink written 8 weeks ago by Carambakaracho270
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