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  • drdna
    Member
    • May 2012
    • 76

    #1

    BLAST missing obvious alignments

    I have been using BLAST to compare genome sequences with the goal of identifying genomic regions that are unique to specific fungal strains. Unfortunately, BLAST misses a large number of long (>1 kb), almost perfect alignments, resulting in too many false positives for my liking. Can anyone recommend another alignment tool that does not miss obvious matches? I know Smith Waterman is more sensitive but I'd like something a little more computationally efficient.
  • maubp
    Peter (Biopython etc)
    • Jul 2009
    • 1544

    #2
    Try turning off the low complexity filter - if part of your query triggers this, that part won't be used in the searches.

    Comment

    • GenoMax
      Senior Member
      • Feb 2008
      • 7142

      #3
      You can also try Blat (http://genome.ucsc.edu/FAQ/FAQblat.html#blat3).

      Comment

      • drdna
        Member
        • May 2012
        • 76

        #4
        I routinely switch off the low complexity filter, so this is not the issue. The problem lies in the initial blast step - breaking the query into short seed "words." Presumably, for long queries, such as genomic contigs, the distribution of the seeds is too sparse.

        Comment

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