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Help understanding this per base sequence content failure fastqc plot

I have this fastqc result from short read WGS data:

enter image description here

I read this post , which suggests that the variation in the first few bases is a known artefact of library prep, so hopefully that bit does not produce concern for my analysis, but what is the variation that starts appearing around base 150 and beyond? Is that concerning? my reads are 150 bp PE. Thanks!

fastqc
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updated by lieven.sterck lieven.sterck • written by curious curious

1 answer

that 151st base added is a base to ignore (it's a kind of random addition) ... if I recall correctly it's a consequence of the technology. There is a post about that as well but I can't immediately find it back.

UPDATE: here is some info in this thread Why does Illumina have the extra +1 cycle? (but that is not the one I was thinking of though)

UPDATE2: to really answer your question: no, not a concern at all. Just clip it off if it's there.

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written by lieven.sterck lieven.sterck

Make this an answer rather than comment?

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written by Mensur Dlakic Mensur Dlakic

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