# About identifying unique sequences

**URL:** https://forum.mothur.org/t/about-identifying-unique-sequences/1809
**Category:** Commands in mothur
**Created:** [April 21, 2014, 11:52pm UTC](https://forum.mothur.org/t/about-identifying-unique-sequences/1809 "2014-04-21T23:52:49Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![Ning](https://avatars.discourse-cdn.com/v4/letter/n/b5e925/32.png) [@Ning](https://forum.mothur.org/u/Ning)
#### Post date: [April 21, 2014, 11:52pm UTC](https://forum.mothur.org/t/about-identifying-unique-sequences/1809/1 "2014-04-21T23:52:49Z")

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Hi,

I was wondering how does mothur identify unique sequences? As unique.seqs() mentioned, it looks for identical sequences.  
If two sequences are different length (length of seq1 \> length of seq2), and seq2 is identical to part of seq1, does mothur see seq1 and seq2 as identical sequences?

If mothur doesn’t see that case as identical sequences, what is the rational reasons?

Thank you very much for any help.

Best  
Ning

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### Author: ![pschloss](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.mothur.org/pschloss/32/4_2.png) [@pschloss](https://forum.mothur.org/u/pschloss)
#### Post date: [April 24, 2014, 10:23am UTC](https://forum.mothur.org/t/about-identifying-unique-sequences/1809/2 "2014-04-24T10:23:28Z")

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To be duplicates the sequences must be the same length and the same sequence. Why? well… that would be a duplicate 🙂

Pat