Question: Tophat2 Mapping Qualities
4
gravatar for geek_y
5.9 years ago by
geek_y10k
Barcelona
geek_y10k wrote:

When I run Tophat2 on human genome, I am using default parameters and with a GTF file from ensemble.

The accepted hits bam file has only three Mapping quality scores in 5th column in my file i.e 0, 3, 50. I would like to know is this correct or I have done something wrong.

As per my knowledge, mapping quality of 0 means the read mapped at multiple places but for other reads, I could see only 3 and 50. The data is from Illumina HiSeq 1000, paired end library.

I would be happy if anybody could help me in figuring out why I am getting only three figures .

bowtie2 tophat2 • 7.4k views
ADD COMMENTlink modified 5.9 years ago by Devon Ryan93k • written 5.9 years ago by geek_y10k

you may also be interested in checking different option for these in tophat2 like -g 1

ADD REPLYlink modified 5.9 years ago • written 5.9 years ago by RT340
6
gravatar for Devon Ryan
5.9 years ago by
Devon Ryan93k
Freiburg, Germany
Devon Ryan93k wrote:

Your results are normal, the MAPQ scores reported by tophat2 are not related to -10*log10(probability the mapping is wrong). It's 50 for uniquely mapped, and then 0-3 for various degrees of multiple mapping.

ADD COMMENTlink written 5.9 years ago by Devon Ryan93k
3

Some addition to the above answer:

255 = unique mapping

3 = maps to 2 locations in the target

2 = maps to 3 locations

1 = maps to 4-9 locations

0 = maps to 10 or more locations.

ADD REPLYlink written 5.9 years ago by Ashutosh Pandey11k

50 means unique mapping for tophat2 ??

ADD REPLYlink written 5.9 years ago by geek_y10k
2

Yeah, they changed from 255 to 50 at some point. I have no clue which release had the change.

ADD REPLYlink written 5.9 years ago by Devon Ryan93k

dpryan79 may be right with that. I haven't used the latest version of tophat2. May be now they score uniquely aligned reads with 50 MAPQ. One reason could be that some downstream tools like GATK complain when they see a MAPQ of 255.

ADD REPLYlink written 5.9 years ago by Ashutosh Pandey11k

Is this documented anywhere?

ADD REPLYlink modified 5.9 years ago • written 5.9 years ago by Fedor Gusev210

Not that I know of. To make life slightly more complicated, the scores used to be 0-3 and 255, so don't be surprised if you see that if you have older datasets.

ADD REPLYlink written 5.9 years ago by Devon Ryan93k
2

I see quality scores of mostly 3 and 50 in recent tophat (2.0.13) but also of 41, 42, 44 and 24, 28

ADD REPLYlink written 5.1 years ago by brentp23k
2

Gotta love undocumented changes.

ADD REPLYlink written 5.1 years ago by Devon Ryan93k
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