# DADA2 detected few representative sequences
**URL:** https://forum.qiime2.org/t/dada2-detected-few-representative-sequences/13825
**Category:** User Support
**Tags:** dada2, feature-table
**Created:** [February 28, 2020, 10:43pm UTC](https://forum.qiime2.org/t/dada2-detected-few-representative-sequences/13825 "2020-02-28T22:43:15Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Max](https://forum.qiime2.org/u/Max)
#### Post date: [February 28, 2020, 10:43pm UTC](https://forum.qiime2.org/t/dada2-detected-few-representative-sequences/13825/1 "2020-02-28T22:43:16Z")
Hi all,
I am new in QIIME2 and I am working with single-end reads that came from Illumina sequencing.
When I used DADA2 I kept with ~70% of total sequences per sample, but for some samples, I obtained few representative sequences. I don't understand exactly how DADA2 cluster the sequences. I know that I'm not discarding sequences from unchimera step because if I sum the detected ASV per sample in the feature table it gives me the number of reads kept after unchimera process.
My line:
qiime dada2 denoise-single --i-demultiplexed-seqs Illumina\_V4.qza --p-trunc-len 0 --p-n-threads 20 --o-table table\_Illumina\_V4.qza --verbose --o-representative-sequences rep\_Illumina\_V4.qza --o-denoising-stats stats\_Illumina\_V4.qza
Am I doing something wrong?
Should I add more trining examples with the option --p-n-reads-learn?
Regards,
Max
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### Author:  [@Nicholas\_Bokulich](https://forum.qiime2.org/u/Nicholas_Bokulich)
#### Post date: [February 29, 2020, 12:29am UTC](https://forum.qiime2.org/t/dada2-detected-few-representative-sequences/13825/2 "2020-02-29T00:29:19Z")
Welcome to the forum @Max!
You should check out the stats file to figure out where you are losing seqs. I strongly suspect you are losing seqs at the pre-filtering stage:
> [@Max](#):
>
> --p-trunc-len 0
Unless if your reads are pristine, you will probably want to truncate (either with this parameter or the `trunc-q` param)... otherwise dada2 will filter out any reads with \> 2 expected errors (by default, see max-ee param), which will probably be many if no truncation was applied.
Give that a spin and let us know how it goes!
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### Author:  [@system](https://forum.qiime2.org/u/system)
#### Post date: [March 31, 2020, 6:29am UTC](https://forum.qiime2.org/t/dada2-detected-few-representative-sequences/13825/3 "2020-03-31T06:29:20Z")
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