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Old 02-13-2014, 02:47 AM   #23
NeleZ
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Location: Germany

Join Date: Dec 2013
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Quote:
Originally Posted by simonandrews View Post
Rory - glad to hear you're liking SeqMonk!

If you've put probes over mRNA features and then done a trend plot then the peak you see at the end might not be due to true 3' bias.

Different transcripts will have exons at different places along their length. Therefore the trend plot for any individual transcript will go up and down as you pass in and out of an exon. If you average over all transcripts then you'll see the combined signals from all of the transcripts doing this which will even itself out for the most part - however the only places you're guaranteed to be in an exon are at the beginning and end of each transcript, so a trend plot over all transcripts will probably show a peak at each end because of the higher probability of being in an exon. Since 3' exons are generally larger than 5' exons you'll probably also see a bigger peak at the 3' end.

What you'd need for a true view of the trend over a spliced transcript would be to concatenate the exons for each transcript together and do a trend plot over those - missing out the introns. This could actually be a good addition to the program so I'll look at adding that in the a future release.

This same problem wouldn't apply to trend plots over exons where you would expect the signal from the reads to be continuous.
@simonandrews
hi, has this option been added yet? I'd also be interested in using it... or would it be possible to have the transcriptome instead of the genome as a reference to remove the up and downs?
or can anyone else help me on how to visualize a 3'/5' bias in my data?
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