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  • statsteam
    Member
    • Sep 2009
    • 19

    TopHat questions

    Hi,

    I have a few general questions.

    I am planning to do the junction mapping using 76bp reads.

    What is the good anchor length to use (I am currently using 5 with a -5 option)?
    Since the reads are long (I used to use 32 bp reads), I am wondering if I can allow more than 3 matches per segment. TopHat currently allows upto 3 mismatches per segment. I initially wanted to set it up with
    --segment-length 76 -- segment-mismatches 4
    but TopHat threw an error saying the number of mismatches is upto 3 per segment. So, I am currently using
    --segment-length 38 --segment-mismatches 2

    Even though my current setting mimics what I wanted to do, it will not be the same as allowing upto 4 mismatches because the 3' end tends to have more sequencing errors.

    Thank you,
    Statsteam
  • colindaven
    Senior Member
    • Oct 2008
    • 417

    #2
    Hi Statsteam,

    I'm new to Tophat but have used Bowtie extensively, which Tophat uses. There is a limit of three mismatches per seed in Bowtie.

    Not sure about your other questions yet.

    Hope that helps

    Colin

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