Question: What causes Linear relations on MAplots?
1
gravatar for Gabriel
5 months ago by
Gabriel50
Paris
Gabriel50 wrote:

Hello I am sort of a newbie in statistical science, so I hope this isn't a terrible question.

I am doing an analysis on example data, and I do the MAplot on my normalized counts from my DESeq2 results. This is what I get: MA plot with a linear relationship

So we have a normal(i think) MAplot, of my two groups, each group has 3 samples.

But in bottom left corner, that is downregulated genes with low read counts we have a linear relation between read counts and Logfold change.

What could cause this?

Are these genes valid?

Another similar phenomena is seen when you compare two samples counts(before any rlog transform): Sample differences with lines at low read counts.

At the low read counts, again we have what looks like straight lines. Does it have something to do with the low sampling rate(counts) of these genes causing aliasing?

Best regards, Gabriel

rna-seq logfold change maplot • 255 views
ADD COMMENTlink modified 4 months ago • written 5 months ago by Gabriel50
1

How to add images to a Biostars post

ADD REPLYlink written 5 months ago by ATpoint21k
1
gravatar for cmdcolin
5 months ago by
cmdcolin1.2k
United States
cmdcolin1.2k wrote:

If you think in terms of algebra a line would be where y/x is a constant.

In the MA plot, Y=log(A)-log(B) and X=log(A)+log(B) so if (log(A)-log(B))/(log(A)+log(B))=constant then this is probably all the values from the gene set A that are 0 or gene set B are 0

ADD COMMENTlink modified 5 months ago • written 5 months ago by cmdcolin1.2k

Thank you. Your answer checks out! I used the identify() function to extract one of the gene names from the lines, and then I checked the raw data. It seems one group had all columns as 0, and the control group had all columns from 50-90 for that specific gene.

ADD REPLYlink written 5 months ago by Gabriel50

Please embed your images properly as suggested above ;-)

ADD REPLYlink written 5 months ago by ATpoint21k

Sorry didn't see it until now, done.

ADD REPLYlink written 4 months ago by Gabriel50
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