Where to find BLAST+ default parameters?
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7.1 years ago
biolab ★ 1.4k

Hi, everyone,

I am using BLAST+ to identify homologous genes. I would like to know the default parameters of BLASTN. When typing blastn -h orblastn -help, I could not find detailed default values. On blast+_user_manual.pdf downloaded from NCBI, I could not find these default settings. Could you please do me a favor? I am particularly concern about word_size, penalty score settings, repeat filter, etc. THANK YOU very much!

blast • 5.3k views
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7.1 years ago
  1. blastn (megablast) [for highly similar sequences]

    • word_size = 10
    • match/mismatch scores = 1, -2
    • gap cost = linear
    • filter = low complexity regions
  2. blastn -task blastn [quite similar sequences]

    • word_size = 11
    • match/mismatch scores = 2, -3
    • gap costs = existence: 5, extension: 2
    • filter = low complexity regions

You can find this information at NCBI BLAST. If you are running local BLAST with outfmt 0 or 1, you will also see the parameters at the end of your output file.

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Thank you a.zielezinski. Your information is useful.

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