Seqanswers Leaderboard Ad

Collapse

Announcement

Collapse
No announcement yet.
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • First base of reads SNP or false result?

    Hi,
    I am using 5 samples pooled DNA Targeted sequencing data (Illumina FASTQ) and using BWA - GATK for mapping and variant calling. In variant calls (vcf files), I find that at aparticular position of genome, first base of the 900 reads (coverage is 1000X) showing mutation (889 out of 900 were showing altered base) but GATK gives very low QUAL score ~40, while highest QUAL in dataset is something about 20,000.

    My question is first base is of high quality base calling and so high altered base count makes it good candidate of mutation. Why does GATK gives so much low QUAL score?

  • #2
    I think the first base is mroe likely to be an error than bases a little further in. Or, you have a PCR mistake that became compounded with PCR duplication. Or those reads are misaligned, and really belong somewhere else.

    A real SNP should show up in a lot of reads that start at a lot of places.

    Comment


    • #3
      Thank you swbarnes2 for explaining why only first base is not so good as variant rather true SNP should be covered by many different reads starting at different positions.

      It is targeted sequencing, one of our targeted exon has 900X coverage and mutational hotspot within that exon was our target. Saying in other ways, when we target a very specific region, amplify using PCR and map them back on genome, obviously they show a similar kind of sequence reads, most of them starting at the same position.

      Coming to the question, in such type of study, should we believe a variant in the very first base of all reads or not?

      Comment

      Latest Articles

      Collapse

      • seqadmin
        Strategies for Sequencing Challenging Samples
        by seqadmin


        Despite advancements in sequencing platforms and related sample preparation technologies, certain sample types continue to present significant challenges that can compromise sequencing results. Pedro Echave, Senior Manager of the Global Business Segment at Revvity, explained that the success of a sequencing experiment ultimately depends on the amount and integrity of the nucleic acid template (RNA or DNA) obtained from a sample. “The better the quality of the nucleic acid isolated...
        03-22-2024, 06:39 AM
      • seqadmin
        Techniques and Challenges in Conservation Genomics
        by seqadmin



        The field of conservation genomics centers on applying genomics technologies in support of conservation efforts and the preservation of biodiversity. This article features interviews with two researchers who showcase their innovative work and highlight the current state and future of conservation genomics.

        Avian Conservation
        Matthew DeSaix, a recent doctoral graduate from Kristen Ruegg’s lab at The University of Colorado, shared that most of his research...
        03-08-2024, 10:41 AM

      ad_right_rmr

      Collapse

      News

      Collapse

      Topics Statistics Last Post
      Started by seqadmin, Yesterday, 06:37 PM
      0 responses
      8 views
      0 likes
      Last Post seqadmin  
      Started by seqadmin, Yesterday, 06:07 PM
      0 responses
      8 views
      0 likes
      Last Post seqadmin  
      Started by seqadmin, 03-22-2024, 10:03 AM
      0 responses
      49 views
      0 likes
      Last Post seqadmin  
      Started by seqadmin, 03-21-2024, 07:32 AM
      0 responses
      67 views
      0 likes
      Last Post seqadmin  
      Working...
      X