Problem when using Fastqc overrepresented sequences to find adapter

Question

[Sean Liang]

Hi all:

I am totally new to NGS data analysis. Recently I am analyzing the small RNA sequencing data from Illumina devices, in the first trim process, I used fastqc to look into the raw data for adapter seeking, and got the overrespresented sequences result as indicated in below picture. I am totally confused about this result and have no idea which sequence is the adapter. Could you please have a look at it for me?

[Michael]

There is a Button Adapter Content, you should check that.

[Sean Liang]

Thanks Micheal, I checked the adaptor content and got this information, does this mean the adaptors have already been trimmed?

[Michael]

This looks good to me. Also, there should not be a standard single end adapter in a small RNA sample. Normally I tend to ignore the overrepresented sequences tab.

[Sean Liang]

Thanks a lot for your help Micheal.