Question: Check if BAM is derived from pair-end or single-end reads?
gravatar for medranom38
2.2 years ago by
Cambridge, MA, USA
medranom3820 wrote:

I'm automating a pipeline and currently a user inputs as a parameter if the input BAM is from pair-end or single-end reads. I want to automatically check this. How can do I this?

single-end pair-end bam • 5.2k views
ADD COMMENTlink modified 22 months ago by John12k • written 2.2 years ago by medranom3820
gravatar for Pierre Lindenbaum
2.2 years ago by
France/Nantes/Institut du Thorax - INSERM UMR1087
Pierre Lindenbaum106k wrote:

use the sam flag and 'samtools view -c -f 1 in.bam ' to test if your bam contains paired reads. ( 1= "read paired" )

ADD COMMENTlink written 2.2 years ago by Pierre Lindenbaum106k
gravatar for ATpoint
22 months ago by
ATpoint3.5k wrote:

You may also use samtools view -H. It will print you the header of the bam, including the command that was used for the alignment. Usually, paired-end data are separated into two fastq files, one for forward/reverse reads. Hence, if the alignment command shows two fastq files to be used, it was a paired-end alignment.

An example where BWA mem was used:

samtools view -H my.bam

@PG ID:bwa PN:bwa VN:0.7.12-r1044 CL:/opt/bwa-0.7.12/bwa mem -M -t 24 /Genomes/hg19/hg19.fasta in_1.fastq in_2.fastq

where the general BWA mem paired-end command is (similar in Bowtie etc.):

./bwa mem -M -t threads indexedRefGenome.fasta in_1.fastq in_2.fastq > out.sam

ADD COMMENTlink written 22 months ago by ATpoint3.5k
gravatar for John
22 months ago by
John12k wrote:

Both methods suggested by Pierre and Alexander will work great for 99.99% of cases, but things get a little messy if you want to detect single-end-reads in a mixed paired & single BAM file, or singletons in a previously paired-end BAM file.

Detecting singles in a mixed file is easy, just look for 'samtools view -c -F 1 in.bam'

Detecting singletons is a bit trickier though... since the filtering step might have just removed the read and left the mate totally unaffected. Perhaps you could use the read names (although people have a habit of putting junk like /1 and /2 on the end of the read names) Or maybe one of Pierre's tools can detect orphaned singletons :)

Alexander's method would solve this very quickly and easily if all BAM files coming in are totally under your pipeline's control (you mapped/filtered them yourself at some point). But external "mystery BAMs" may have issues.

ADD COMMENTlink modified 22 months ago • written 22 months ago by John12k
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