Unconfigured Ad

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • tahamasoodi
    Success
    • May 2012
    • 130

    #1

    Problem with Sequence Quality using FastQC

    I have whole genome data in paired end fastq files. Before going for its alignment, I checked some of the samples for quality using FastQC but I'm getting strange results as seen in the attachments. Shall I move ahead with such data or need to trim these sequences or discard the data? I've majority of samples like this!

    Click image for larger version

Name:	per_base_quality.png
Views:	1
Size:	11.5 KB
ID:	307936

    Click image for larger version

Name:	per_sequence_quality.png
Views:	1
Size:	22.1 KB
ID:	307937

    Click image for larger version

Name:	per_base_sequence_content.png
Views:	1
Size:	20.6 KB
ID:	307938

    Click image for larger version

Name:	duplication_levels.png
Views:	1
Size:	18.1 KB
ID:	307939

    Click image for larger version

Name:	kmer_profiles.png
Views:	1
Size:	48.3 KB
ID:	307940
    Thanks,
  • Apexy
    Member
    • Apr 2011
    • 62

    #2
    Hi,

    I would suggest you trim the leftmost part of the sequences. Given that you still have some high quality bases at the 3'-end, it will be good to set a Q-score threshold during trimming. By doing this you will end up with reads of varying lengths.
    http://www.youtube.com/watch?v=bz93ReOv87Y

    HTH

    Comment

    • tahamasoodi
      Success
      • May 2012
      • 130

      #3
      Thanks, what about the sequences which ll be trimmed? Doesn't it has any impact on the results?
      Thanks,

      Comment

      • Apexy
        Member
        • Apr 2011
        • 62

        #4
        Which ever method you use should enable you retain the high quality 5'-ends of trimmed reads.

        Comment

        • chadn737
          Senior Member
          • Jan 2009
          • 392

          #5
          I am not sure how much trimming will help you as your quality declines pretty rapidly and not very far into the reads. Try it, but I would also point this out to who ever did the sequencing (assuming it wasn't you).

          Comment

          • simonandrews
            Simon Andrews
            • May 2009
            • 870

            #6
            Your Kmer plot suggests that a reasonable proportion of your library contains very short inserts (we can't really tell what proportion from the graph - you'd need the accompanying table for that).

            Is it possible you've just made a library with extremely short inserts and that this is why the quality is dropping so quickly? Given the adapter contamination you probably need to adapter trim your data anyway for it to be of any use, so you might as well quality trim while you're at it.

            Comment

            Latest Articles

            Collapse

            • SEQadmin2
              Multiomic Liquid Biopsy: What DNA/RNA Panels Reveal That DNA Alone Can’t
              by SEQadmin2



              Tumors contain complex mixtures of cell populations that evolve in response to treatment and host-specific factors. Tissue biopsies provide only static snapshots of a tumor’s state. But what if we could follow that evolution over time using a minimally invasive technique?

              Liquid biopsies can detect tumor-derived material circulating in the bloodstream, providing a way to study treatment response, detect emerging resistance, and discover new biomarkers. Circulating
              ...
              10-14-2026, 09:55 AM
            • SEQadmin2
              New Genomics Technologies Take Aim at Long-Standing Limits
              by SEQadmin2


              Researchers using sequencing and genomics tools often have to make trade-offs. They can choose between speed or scale, short reads or long-range information, or targeted panels or a view of the whole transcriptome. New technologies that have been released this year are built to address those tough choices.

              We asked six companies the same four questions to learn about their latest products. The new technologies bring a lot to the table, including rethinking sequencing
              ...
              09-28-2026, 10:25 AM

            ad_right_rmr

            Collapse

            News

            Collapse

            Topics Statistics Last Post
            Started by SEQadmin2, 10-15-2026, 10:52 AM
            0 responses
            23 views
            0 reactions
            Last Post SEQadmin2  
            Started by SEQadmin2, 10-14-2026, 05:39 AM
            0 responses
            27 views
            0 reactions
            Last Post SEQadmin2  
            Started by SEQadmin2, 10-13-2026, 09:56 AM
            0 responses
            23 views
            0 reactions
            Last Post SEQadmin2  
            Started by SEQadmin2, 10-09-2026, 11:14 AM
            0 responses
            28 views
            0 reactions
            Last Post SEQadmin2  
            Working...