Are both samtools mpileup options -m and -F only related to indel detection?
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3.8 years ago
serpalma.v ▴ 70


I am a beginner in variant calling with samtools and trying to understand its usage. Often the options -m and -F are used, together with the option -p. This is what appears in the documentation for samtools mpileup:

  -p, --per-sample-mF     apply -m and -F per-sample for increased sensitivity
  -m, --min-ireads INT    minimum number gapped reads for indel candidates [1]
  -F, --gap-frac FLOAT    minimum fraction of gapped reads [0.002]

-m is explicit and it applies to indel detection, whereas -F deals with gapped reads, which I guess applies to indel detection as well. Also, since -p applies both options per-sample, I would guess that they address the same type of analysis (indel detection).

My questions are:

  • Do both -m and -F apply to indel detection and have nothing to do with SNP detection?

  • How to interpret the default value of -F. Is it correct to say that out of 500 reads overlapping a genomic region at least 0.002*500=1 reads should be gapped in order to do indel related calculations?

  • What if -mis TRUE and -F is not? (i.e. there is 1 gapped read, but 505 reads overlap the region).

  • When would I want to modify the default values? It seems that the defaults are very low.


mpileup samtools next-gen alignment SNP • 947 views

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