Project level VCF

I am combining gVCFs that are processed exactly the same, I observed that most variants have this tag: "GT:AD:DP:GQ:PL". However for some variants, within the same variant, they can have this tag GT:AD:DP:GQ:PGT:PID:PL" for some of the samples but not others.

I did some testing
a) perform combineGVCF on a set of gVCF then do genotypeGVCF (test a)
b) perform genotypeGVCF only on this set of gVCF (test b)

What I observed is that there are some variants present only in test a, but not in test b. Same thing happens vice versa, i.e. variants present only in test b, but not in test a. These kind of variants all all got the same tag GT:AD:DP:GQ:PGT:PID:PL. Why is this the case? And what is combineGVCF and genotypeGVCF actually doing?

Answers

  • Geraldine_VdAuweraGeraldine_VdAuwera Cambridge, MAMember, Administrator, Broadie
    We'll address the question about additional variants in the output in your other discussion thread.

    The tag differences you observe are due to some variants getting additional annotations that can be added when there are multiple variants within an active region. They are related to physical phasing. For more on this, please read the HaplotypeCaller documentation.
  • Thanks for your comments.

    1) How would the phasing information affect the way the variants are being combined across different samples?

    2) how should we handle phasing information when generating project level VCF?

  • SheilaSheila Broad InstituteMember, Broadie, Moderator

    @yyee
    Hi,

    I don't think the phasing affects the way variants are combined across the samples. Can you please post some example records from the GVCFs and from testing a and b like you mentioned above. Specifically, I need to see the GVCF record from HaplotypeCaller and how the record differs after CombineGVCFs and GenotypeGVCFs.

    Thanks,
    Sheila

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