A strange R limma voom function mean-variance trend

Question

[shanika.amarasinghe]

Hi to the experts,

I am new to RNA-Seq analysis and tried using limma on my data. After voom transformation, I get something like in the image attached. I double checked the metadata used for creating the DGElist and they all seem fine. Has anybody seen a trend like this? I cannot figure out what might be causing this. If you could please explain, would be more than great. I am really stuck in this and want to get out of it so badly... The link to the image is here: https://drive.google.com/open?id=0Bx6HyClNrtOXS1RpMnJYUE9ZZEk

Thanks a lot in advance.

[Jautis]

OP, did you ever figure this out? I see something similar if I don't filter out lowly expressed genes but do still see a strong positive relationship after doing so

Answer 1

[shanika.amarasinghe]

Hi all,

I managed to find out the reason behind this. I have used improperly mapped BAM files in the initial steps. I reckon it's a rookie mistake that no one should do, but could happen if you are as careless as me. So trying to double check the BAM file quality after mapping would save you from lots of heartache.

Cheers!

[jake.hagen]

For future reference I wasn't able to view your image, it wanted me to sign in. Maybe it needs to be shared differently, or maybe it is just me.

[shanika.amarasinghe]

I'm really sorry about that. Yes there was a permission problem with it. Thank you for pointing it out.