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# ReduceReads - No real operator (M|I|D|N) in CIGAR

Posts: 93Member

Hi. When I reduce my BAM files with ReduceReads and then run HaplotypeCaller I get this warning:

Ignoring SAM validation error: ERROR: Read name 1060, No real operator (M|I|D|N) in CIGAR

Why is this? Is it OK to inore it?

Tagged:

This sounds like the aligner was sleeping on the job... If it's just a few reads, I'd ignore it, or maybe use -rf BadCigar to filter them out so we don't risk choking on them later on. If it's more than a few, by all means check the alignments throughout the file.

Geraldine Van der Auwera, PhD

• Posts: 4Member

Dear Geraldine,
Thanks and regards.

Hi @taojinsheng,

"sleeping on the job" is a colloquial phrase that means "doing something wrong". In this case it means that the aligner produced invalid output.

One easy way of knowing how many reads are affected is to run the CountReads tool with the BadCigar filter enabled, like this:

java -jar GATK.jar -T CountReads -R ref.fasta -I reads.bam -rf BadCigar


When the run finishes, there will be a line in the console output that tells you how many reads were filtered out by BadCigar.

If the percentage of bad reads is high, then you may need to do additional QC on your data and possibly realign them from the original FastQ.

Geraldine Van der Auwera, PhD

• Posts: 4Member

I got it.Thanks a bunch,Geraldine.