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mpileup: specified region truncated.



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  • mpileup: specified region truncated.

    Hello gentlepeople,

    I am using the samtools 'mpileup' program.
    I wish to generate a pileup file for a specific region.
    I have several separate .bam input files that I am generating the pileups for.
    Unfortunately, mpileup truncates the region and I only get data for the first part of the region.
    I have ran the same command on different .bam files and get different results.

    When I command:

    samtools mpileup -f 'hg19.fa' -r chr6:27114408-27115845 'experiment01.bam' > out_PILEUP2.pile
    [mpileup] 1 samples in 1 input files
    <mpileup> Set max per-file depth to 8000

    I get a file with 746 lines.
    I am expecting 1438 lines because that is the size of the interval I have specified with the '-r' flag
    If I use mpileup with the same region but with a different .bam file I get a different size file.

    samtools mpileup -f 'hg19.fa' -r chr6:27114408-27115845 'experiment02.bam' > out_PILEUP3.pile
    [mpileup] 1 samples in 1 input files
    <mpileup> Set max per-file depth to 8000

    I get a file with 623 lines.
    Again, I am expecting 1438 lines because that is the size of the interval I have specified with the '-r' flag.

    The first line in both files is for chr6:27114408, as expected.
    BUT, the files are truncated at different positions.
    With experiment01.bam the final line of the pileup file is chr6:27115577.
    With experiment02.bam the final line of the pileup file is chr6:27115344.

    This must have something to do with the .bam file.
    Can someone tell me which parameter needs to be adjusted?
    I have consulted the manual but I could not identify anything that sounded applicable.

    Thanks for you time,
    Lionel (Lee) Brooks 3rd
    Dartmouth Genetics Grad Student

  • #2
    The simplest answer is that you just don't have any reads across part of your region.

    Try getting the .sam file for the same region +- 500 bases, or try looking at the whole .bam in IGV. You can zoom in on your region.


    • #3
      Yeah, mpileup doesn't generate lines for regions it has no reads on. If you need to work out whole-region coverage, then you should be looking at the column that gives the base number. For covered regions, this will increase by 1 per line (assuming no inserts), but will jump multiple bases when there are no reads.


      • #4
        whoops, should have checked that...thanks!


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