# loosing reads after dada2 filteration

**URL:** https://forum.qiime2.org/t/loosing-reads-after-dada2-filteration/32373
**Category:** General Discussion
**Created:** [January 23, 2025, 12:28am UTC](https://forum.qiime2.org/t/loosing-reads-after-dada2-filteration/32373 "2025-01-23T00:28:47Z")
**Posts on this page:** 1
**Showing post:** 8

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### Author: ![colinbrislawn](https://forum.qiime2.org/user_avatar/forum.qiime2.org/colinbrislawn/32/6221_2.png) [@colinbrislawn](https://forum.qiime2.org/u/colinbrislawn)
#### Post date: [January 25, 2025, 4:12pm UTC](https://forum.qiime2.org/t/loosing-reads-after-dada2-filteration/32373/8 "2025-01-25T16:12:40Z")

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Here is one last clue that may be related to your problem:

It's by benjjneb, who is the developer of DADA2, and related to the V3-V4 primers, like you are using:

> [@Questions about V3–V4 primers for 16S rRNA amplicon sequencing, and calculating overlap](https://forum.qiime2.org/t/questions-about-v3-v4-primers-for-16s-rrna-amplicon-sequencing-and-calculating-overlap/20250/2):
>
> Yes, there is variation in lengths of 16S segments. It isn't large, but it exists. In particular, there are two modes of V3V4 length in nature, one at 460 nts and another ~440 nts (using these primers). So you'll want to make sure even the longer natural amplicons will sufficiently overlap after truncation.

If these 8 samples happen to have lots of microbes with the longer ~460 bp amplicon, then they need that extra length to merge.

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