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Sequece Raw Data QC A/T.G.C Distribution

Hi, Recently we got our samples sequenced. Fungal samples. Sequenced with illumina-PE

Although we got really really good Data quality with illumina, Image below Distribution of sequence qiality

but in the Distribution of A/T/G/C graph, there are things which I am not able to understand completly.

Ideally the distribution between AT/GC should be similar as they ate suppost to be equal in numbers. (right ?)

but in one of my samples it looks like this. Distribution of A/T/G/C Base

my question is

  1. Why the distribution graph looks like this actoss the bases ?
  2. WHy it is fluctuating so much in tha start and in the middle.

Thank You

illumina sequencing fastqc
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updated by GenoMax GenoMax • written by SomeOne • SomeOne

1 answer

Please read this for more:

https://sequencing.qcfail.com/articles/positional-sequence-bias-in-random-primed-libraries/

PolyA capture libraries show a bit of bias for A/T.

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written by GenoMax GenoMax

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