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

Question

[Umer]

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

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.

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

Answer 1

[GenoMax]

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.

[Umer]

Thanks. Its helpful