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Galaxy DNA-Seq Tutorial

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=== Results ===
 
=== Results ===
  
 +
* Take the trimmed data and run again compute quality statistics and draw the boxplot
 
[[File:Cmv21950r 3 1 trimmed boxplot.jpg]]
 
[[File:Cmv21950r 3 1 trimmed boxplot.jpg]]
 +
* Results should look like above if everything was done correctly
  
 
== Short read alignment to reference genome using BWA ==
 
== Short read alignment to reference genome using BWA ==

Revision as of 14:46, 15 September 2011

Contents

Galaxy DNA-Seq Tutorial

Linking to data

Link in the Mark Pritchard Vaccinia virus data set.

  • Start with a blank history, there should be no numbered items on the right hand side of the pane. Otherwise create a new history.
  • Select "Shared Data" from the top of the screen to bring up the Shared Data screen
  • Select Data Library
  • Select "Pritchard Vaccinia WR FastQ Files" from the alphabetically sorted list

DataLibraryVacWRFastQ.jpg


  • Click on the subfolder top box to select all 6 files
  • Select "import to current history"
  • Click on "Analyze Data" from the upper main menu. It should bring up the main page and your history pane should now look like the image below.

HistoryPane.jpg

  • Notice that with just 3 viruses are already over 4 GB of data!


Formatting and Grooming Data

  • Your data is often NOT what you expect

FastQ Format

  • FastQ format can mean many things, see the wikipedia entry on FastQ format
  • Ilumina FastQ format also not informative, it changes
  • Click on the pencil to icon in one of the virus images to pull up the attributes, your screen should look a bit like this:

DataType.jpg

  • In Galaxy the expected data type of the galaxy tool must match EXACTLY with the data type in your history pane, otherwise the option to use that particular piece of data will not appear in the tool's drop down menu for data selection.
  • Galaxy requires that everything go into Sanger format to be used. If you know your data is in sanger format, select fastqsanger for your data type. If it is not in that format, select fastq and run the FastQ Groomer.
  • FastQ groomer is very useful, but slow
  • Not a bad idea to run it if you are dealing with a new machine and have the time. Costly in terms of space.

Reference Genome

  • Ensure the correct reference genome is selected
  • WARNING - seeing the reference genome doesn't mean it is there for using
  • The current list of genomes available at UAB is here
  • Contact the UAB Galaxy team or me if you need a genome added (similar procedure for Penn State)
  • Used for a variety of tools, it can be overridden earlier
  • Any problems with CMV-21950R_3_1.fastq ?

Assessing the quality of the data

We will use a number of different tools from the "NGS: QC and manipulation" drop down menu. Try processing the FastQ files with:

  • FastQC
  • Compute Quality Statistics


Running FastQC

FastQC gives an attractive visual output and will flag potential problems.

  • Select NGS: QC and manipulation -> FastQC

FastQCRunSettings.jpg

  • Run it on all the fastq files
  • Remember, you are on a cluster, this can be done in parallel

FastQC Results

Take a look at the other areas that show up as quality issues.

  • FastQC flags potential problems
  • Are there any problems for us?

CMV VAC WR 3 2 base quality.jpg

  • It is imperative to understand your organism and its biology to interpret the data

Running Quality Statistics and Boxplot

  • Galaxy has its own set of tools for computing quality statistics (using R)
  • Generates raw statistics in tabular format which can then be used for a pretty box plot
  • Select NGS: QC and manipulation -> Compute Quality Statistics for CMV-21950R_3_1.fastq
  • Run it to compute the tabular file

RunComputeQualityStats.jpg

  • Why wait? Jobs can be queued, so go ahead and queue up a box and whiskers plot
  • "NGS: QC and manipulation" -> Draw Quality Score Boxplot
  • Can run it on "Data 13" (or whatever) even if Data 13 doesn't exist yet / isn't ready

DrawQualityScoreBoxplot.jpg

Quality Statistics and Boxplot Results

  • Should have a tabbed result file that is easy to manipulate in Galaxy

QualityStatsResults.jpg

  • Should get a nice box and whiskers plot

Cmv21950r 3 1 original boxplot.jpg

  • Problems with this data? How does it compare to FastQ?

Trimming Reads

  • About a quarter of the last base is of poor quality
  • Trim off the 3' end

FastQTrimmerRun.jpg

  • There are other ways to clean up, reads can be filtered by other criteria
  • What to keep and what to throw away depends on your requirements

Results

  • Take the trimmed data and run again compute quality statistics and draw the boxplot

Cmv21950r 3 1 trimmed boxplot.jpg

  • Results should look like above if everything was done correctly

Short read alignment to reference genome using BWA

Bwa run cmv 227r.jpg

BAM Conversion

The output of many mapping programs is in SAM format and must be converted to the binary format. The conversion is lossless. Flagstat.jpg

Sam2bam.jpg

Variant Analysis

Samtools

  • Essential toolset, performs a variety of functions including generation of a "pileup" file.

GeneratePileup.jpg

Other Variant Detection Approaches

  • GATK - Emerging as the new best practise to call variants, not integrated into Galaxy just yet.
  • SNPEff
  • PATRIC, annotation sites

SNPEff and Variant Summation

Summarizing variants and effects of SNPs.

  • Reference genome must be in SNPEff, need GFF3 file of your genome annotation
  • SNPEff looks at heterozygous and homozygous SNPs, MNPs
  • Plots coverage, indel sizes

Running SNPEff

SNPEff.jpg


Results from SNPEff

  • Only as good as your genome annotation file
  • Introns in viruses?

SNPEffCoverage.jpg

SNPEffResults.jpg


Locating Relevant SNPs versus Control

FilterRunVacWR.jpg

PileupFiltering100Reads.jpg


De novo assembly (time permitting)

Viewing results in IGV