So what could possibly have introduced that 'N' into the sequence reads ? 
Is it present in the original .fastq file ?

                                                        -  tom blackwell  -

On Tue, 4 Nov 2014, Arumilli, Meharji wrote:

> Hi,
>
> These are the commands used to call variants using  samtools-0.1.19:
>
> samtools mpileup -ABugf ref.fa -l bed -d 1000000 bam | bcftools view -vcg - | 
> vcfutils.pl varFilter -D 1000000 > out.vcf
> vcfutils.pl varFilter -Q 40 -d 10 out.vcf | awk '$6>=40' > fin.vcf
>
>
> Hope this might help to some extent.
>
>
> On 04/11/14 20:52, Thomas W. Blackwell wrote:
>> 
>> As with the earlier question, we are all puzzling what could possibly have 
>> introduced N's into the sequence reads.  No details of upstream processing 
>> steps are given, so no one has any ideas to contribute. Simplified command 
>> lines and software version numbers are always helpful.
>>
>>                                   -  tom blackwell  -
>> 
>> On Tue, 4 Nov 2014, Arumilli, Meharji wrote:
>> 
>>> Hi,
>>> 
>>> 
>>> I have performed variant calling with samtools. For, some reason some of 
>>> the variants have N in ALT column as shown below:
>>> 
>>> Chromosome      Position        SNPid   Reference Alternate       QUAL MQ 
>>> DP
>>> chr21    29989187    .    A    AN    96.50    60    46
>>> 
>>> This is a homozygous mutation supported by 46 reads with MQ of 60.
>>> 
>>> Checked the bam file for this position using mpileup
>>> 
>>> samtools mpileup -AB -f ref.fa -r chr21:29989186-29989188 input.bam
>>> 
>>> The output is
>>> 
>>> chr21    29989187    A    49 
>>> ....,,,,..,,,,+1n,,...,,,,..,,,,,...,,,...,..,,.,.,^]. 
>>> 7BF<<FFFB7FF<0FIFIIIFBFIIBFFF<IIIFFB<IIFII7BIBIBB
>>> 
>>> Is this a bug in the code that it is called as "AN" insertion. How should 
>>> i infer this mutation.
>>> 
>>> Any comments from the users of this community are highly valuable.
>>> 
>>> 
>>> Br
>>> Mehar
>>> 
>>> 
>
>

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