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  • nrnoyes
    Junior Member
    • Sep 2013
    • 5

    #1

    Reconciling bwa XA: field

    Hello,

    I am in the process of trying to understand bwa output, so excuse this question if it is very naive.

    I have used the -n option with sampe in order to output all alternative hits. In several instances, the "best hit" for a read (not sure what to call it since it's not actually the "best") is the same reference sequence as the "alternative hit", although the "best hit" is coded as "XT:A:U" in the XT field. I interpret this as meaning that this read has more than one equally-good hit, but it's still a unique hit, and furthermore the two equally-good hits are the same.

    The only way I can explain this is that the read aligns to the same reference sequence, BUT at two "equally-good" locations within the reference sequence.

    Can anyone confirm that this is, in fact, the case with these reads?

    Thanks very much,

    Noelle
  • TiborNagy
    Senior Member
    • Mar 2010
    • 329

    #2
    A read can not be unique, if it has more than one equally good hits. The -n argument is just set the maximum number of alignments.

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