Weird 8bp peak in (clean) small RNA data?

01 January 1970 0 10K Report

Hi everyone,

I've received some small RNA sequencing data from a collaborator and after removing adapter and trimming (with TrimGalore) i have a small peaks at ~20 and 30 bp, as I was expecting, plus a huge peak at 8bp that contains most of the bases of the sequencing. There are no overepresented sequences in the samples and they used the NEXTFLEX® Small RNA-seq. This is a whole insect sample. I saw a lot of unexpected lenght peaks in small RNA sequencing but never at 8bp and I have no idea what that is, it is present in all the samples they received. Does anyone with more experience than me know what this 8bp sequences may be?

Attached is the fastqc length distribution graph

Thanks and have a nice day!

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