Insertions follow reference in vcf file

josk

Junior Member

Join Date: Oct 2011
Posts: 1

Insertions follow reference in vcf file

12-15-2022, 07:20 AM

Hi,
I'm working with gvcf files, containing also non-variant positions. I have noticed some insertions that I'm not able to correctly interpret or handle. An example (simplified):

Code:

NC_013991.2 1403 . G GAA 176.32 . GT:AD:DP:GQ:PGT:PID:PL:PS ./. 0/0 0/0 ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. 1|1 0/0 ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. 0/0 ./. ./. 1/1 ./. ./. 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 ./. 0/0 0/0 0/0 0/0 ./. 0/0 ./. 0/0 ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./.
NC_013991.2 1404 . A . . . GT:AD:DP:RGQ ./. 0/0 0/0 0/0 ./. ./. ./. ./. ./. ./. ./. 0/0 ./. ./. ./. ./. 0/0 ./. 0/0 0/0 0/0 ./. ./. ./. ./. ./. ./. 0/0 ./. ./. ./. ./. ./. ./. 0/0 0/0 0/0 0/0 ./. ./. 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 ./. 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 ./. 0/0 0/0 0/0 0/0 ./. ./. ./. 0/0 ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. 0/0 ./. ./. ./.
NC_013991.2 1405 . A . . . GT:AD:DP:RGQ ./. 0/0 0/0 0/0 ./. ./. ./. ./. ./. ./. ./. 0/0 ./. ./. ./. ./. 0/0 ./. 0/0 0/0 0/0 ./. ./. ./. ./. ./. ./. 0/0 ./. ./. ./. ./. ./. ./. 0/0 0/0 0/0 0/0 ./. ./. 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 ./. 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 ./. 0/0 0/0 0/0 0/0 ./. ./. ./. 0/0 ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. ./. 0/0 ./. ./. ./.

Here, the reference sequence is "GAA". Why, at site 1403, do I get an alternative allele "GAA"? There seem to be two samples at this position that are "1/1", thus homozygous for GAA. But they are also homozygous for A at the next positions. What thus is their genotype ? GAAAA, thus containing an insertion of AA?
I've seen multiple cases like this, also with longer alternative alleles, and each time the alternative allele sequence exactly recapitulates the reference sequence. This seems like an error to me, but how to correct?
The mapping was done either with bwa aln or bwa mem, and we've observed this behaviour both when using GATK4 and bcftools for genotyping.

I would be very grateful if someone could clarify this.
Thanks,
Jos

Tags: bcftools, bwa, gatk, mapping, vcf

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