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calling variants in multiple samples

i have sequenced two exomes from two affected individuals from the same family.
i have called their variants with the recommended UnifiedGenotyper protocol for each sample individually (was done a year and half ago..), and then did theintersection to find teh shared ones.
i was wondering, if you recommend calling them at one step, togther? is there any added value for doing so (in term of reducing false positives, accuracy etc..).

Answers

  • CarneiroCarneiro Charlestown, MAMember admin

    It is always better to call samples together to empower filtering. However in a 2 sample situation the gains may not be all that significant. It never hurts though.

  • galmorangalmoran Member

    thanks for your quick reply!
    so, what command should i be using?
    the analysis is only joined at the var call step (i.e, the processing of BAM files - local realignment, variant qaulity recalibration etc.. is done separately?). it should be noted they were sequenced in different experiments...
    i also see that since i've used GTAK last time, you have indtroduced the HaplotypeCaller. should i used it instead of UnifiedGenotyper?

    and last question, if you are willing to elaborate - what is exactly achieved when i call multiple samples stimultaneosly in one command?
    does it compare or filter them based on the comparison? (especially if they were not sequenced toegther)
    Moran

  • Geraldine_VdAuweraGeraldine_VdAuwera Cambridge, MAMember, Administrator, Broadie admin

    Hi Moran,

    Multisample calling is addressed in the UnifiedGenotyper documentation and in many other posts on this forum. Please have a look through that and if you have any remaining questions we'll be happy to answer them.

    If your samples are diploid you should give the HaplotypeCaller a shot, yes. the indel results in particular will be much better. Multisample calling is achieved the same way with the HC as with the UG.

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