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  • murphycj
    Member
    • Sep 2011
    • 10

    #1

    SNP/indel quality

    Hi,

    Aim:
    I' am comparing mpileup/bcftools and UnifiedGenotyper.

    My data:
    7 samples. Reads aligned with tophat against hg19.

    Result:
    Average 'QUAL' in vcf files: UnifiedGenotyper (404), mpileup/bcftools (28).
    Average snp/indel calls: UnifiedGenotyper (49,739), mpileup/bcftools (253,933).

    Issue:
    Greater than 90% of the tophat-mapped reads had MAPQ of 255. Therefore, when using UnifiedGenotyper, I had to use:"-rf ReassignMappingQuality -DMQ 60".

    Question:
    Can I compare the 'QUAL' field in the vcf output call sets from GATK and SAMtools? My intuition says no. However, I realize GATK uses MAPQ as a cap on base quality. So if anything, the 'QUAL' values for GATK calls are low. I' am still looking into how the SNP/indel calling algorithms use MAPQ.

    Any input would be helpful. I' am a novice. Also, I should maybe redo the tophat alignment for correct MAPQ.

    Best.

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