Question: how to confirm that mapped read are accurate?
gravatar for marongiu.luigi
12 months ago by
Germany, Mannheim, UMM
marongiu.luigi520 wrote:


I have aligned my reads against the reference genome using BWA, I removed the reads with low quality and deduplicated the alignment. How do I now that the results are correct?

Do I need to prove that the reads are mapped correctly by using a second aligner (which should confirm the results of BWA)? This approach I actually did not see it anywhere.

Essentially, I do I know that I am not using garbage? What is the consensus on quality control of the mapping?

Thank you

ADD COMMENTlink written 12 months ago by marongiu.luigi520

if you did not mess up BWA parameters nor the pre-processing of reads, I would go by "if it maps, it maps"!

What set you off for this question anyway? Did you notice anything weird in the results (or using the results?)

ADD REPLYlink written 12 months ago by lieven.sterck8.5k

Well, I wouldn't like that the reviewer comes with some 'below the waterline' question after all this work, so I' rather be sure of the data I gathered. The main problem is that I am aligning against a mix human-virus reference: I need to be sure that the reads are mapped against the virus genome and not against a virus that is actually homologous of a human sequence mistakenly identified as viral. The number of reads mapping the viral genome is very small (and this is comprehensible, assuming that the viruses are very few in the sample), which does not help, and some reads look like split into something else. For instance, this looks OK: enter image description here but this one? can I trust it? enter image description here and this? enter image description here (I have a triad of normal/cancer/metastasis)

ADD REPLYlink modified 12 months ago • written 12 months ago by marongiu.luigi520

Are there any regions in the human genome that are very similar to your virus of interest? If you use the viral genome you used as a a reference and cut it up into fake "short read" sequences and align it against the human, where do they go? And what are the alignment scores of the real reads that align to your virus genome compared to the alignment scores of those exact same reads when aligned to the human genome?

If you want to show that the virus genome is a better fit than the human genome, then you gotta show that the alignment scores/edit distances reflect that.

ADD REPLYlink written 12 months ago by Friederike6.0k

good point! I'll try it...

ADD REPLYlink written 12 months ago by marongiu.luigi520
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