SeqShop: Variant Calling and Filtering for SNPs Practical, June 2014

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Goals of This Session

  • What we want to learn
    •  How to generate filtered variant calls for SNPs from BAMs
    • Basic variant call file format (VCF)
    •  How to examine the variants at particular genomic positions
    •  How to evaluate the quality of SNP calls

GotCloud SnpCall Pipeline

SnpcallDiagram.png

Why GotCloud?

Many of the same reasons as using GotCloud align

  • Easy to learn & run
    • All-in-one package for snp calling pipeline
    • You don’t have to know the details of individual component
  • Robust parallelization
    •  Automatic partitions by regions
    •  Reliable and fault-tolerant parallelization via GNU make
      • Restart from where it stopped upon unexpected crash
  • Cloud & Cluster-friendly
    • Supports multiple clusters such as MOSIX, Slurm, & SGE
    • Amazon instances allow running large-scale jobs without having your own cluster
  • Easy to add new samples to your study
    • Just add them to your index
    • GotCloud will reuse the genotype likelihoods for samples already completed


Login to the seqshop-server Linux Machine

This section will appear redundantly in each session. If you are already logged in or know how to log in to the server, please skip this section

  1. Login to the windows machine
    • The username/password for the Windows machine should be written on the right-hand monitor
  2. Start xming so you can open external windows on our Linux machine
    • Start->Enter "Xming" in the search and select "Xming" from the program list
    • Nothing will happen, but Xming was started.
    • View Screenshot

      • Xming.png

  3. Open putty
    • Start->Enter "putty" in the search and select "PuTTY" from the program list
    • View Screenshot

      • PuttyS.png

  4. Configure PuTTY in the PuTTY Configuration window
    • Host Name: seqshop-server.sph.umich.edu
    • View Screenshot

      • Seqshop.png

    • Setup to allow you to open external windows:
      • In the left pannel: Connection->SSH->X11
        • Add a check mark in the box next to Enable X11 forwarding
        • View Screenshot

          • SeqshopX11.png

    • Click Open
    • If it prompts about a key, click OK
  5. Enter your provided username & password as provided


You should now be logged into a terminal on the seqshop-server and be able to access the test files.

  • If you need another terminal, repeat from step 3.

Login to the seqshop Machine

So you can each run multiple jobs at once, we will have you run on 4 different machines within our seqshop setup.

  • You can only access these machines after logging onto seqshop-server

3 users logon to: 

ssh -X seqshop1

3 users logon to: 

ssh -X seqshop2

2 users logon to: 

ssh -X seqshop3

2 users logon to: 

ssh -X seqshop4

Setup your run environment

This will setup some environment variables to point you to the Tutorial files as well as to an output directory. 

source /home/mktrost/seqshop/setup.txt

Alternatively, if you would like to change the output directory, copy the file, make the modifications and source your file: 

cp /home/mktrost/seqshop/setup.txt ~/setup.txt
nedit ~/setup.txt
source ~/setup.txt

(You can use your favorite editor instead of nedit. I typically use emacs, but nedit is more like Windows.)


Examining GotCloud SnpCall Input files

Sequnce Alignment Files: BAM Files

Reference Files

GotCloud BAM Index File

GotCloud Configuration File

We will use the same configuration file as we used yesterday in GotCloud Align.


Run GotCloud SnpCall

Now that we have all of our input files, we need just a simple command to run: 

${GC}/gotcloud/gotcloud snpcall --conf ${GC}/inputs/gotcloud.conf --numjobs 4 --region 22:36000000-37000000
  • --numjobs tells GotCloud how many jobs to run in parallel
    • Depends on your system
  • --region 22:36000000-37000000
    • The sample files are just a small region of chromosome 22, so to save time, we tell Gotcloud to ignore the other regions

This should take about 5 minutes to run.

It should end with a line like: TBD

If you cancelled GotCloud part way through, just rerun your GotCloud command and it will pick up where it left off.

Examining GotCloud SnpCall Output

Filtering Summary Statistics

cat ${OUTPUT}/vcfs/chr22/chr22.filtered.sites.vcf.summary

View Annotated Screenshot

FilterSum.png


GotCloud Genotype Refinement

seqshop/gotcloud/gotcloud beagle --conf seqshop/inputs/gotcloud.conf --numjobs 2 --region 22:36000000-37000000
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