BIOL368/F14:Week 12

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BIOL368: Bioinformatics Laboratory

Loyola Marymount University

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This journal entry is due on Tuesday, November 18 at midnight PST (Monday night/Tuesday morning). NOTE that the server records the time as Eastern Standard Time (EST). Therefore, midnight will register as 03:00.

Note that the due date has been moved up one day to Tuesday at midnight so that the instructor can review your assignments before class on Wednesday.



Overview of DNA Microarray Analysis

This is a list of steps required to analyze DNA microarray data.

  1. Quantitate the fluorescence signal in each spot in the microarray image.
    • Typically performed by the scanner software, although third party software packages do exist.
    • The image of the microarray slide and this quantitation are considered the "raw-est" form of the data.
    • Ideally, this type of raw data would be made publicly available upon publication.
    • In practice, the image data is usually not made available because the raw image file of one slide could be up to 100 MB in size.
    • Also, some journals do not require data deposition as a requirement for publication, so often published data are not actually available anywhere for download.
    • Microarray data is not centrally located on the web. Some major sources are:
  2. Calculate the ratio of red/green fluorescence
  3. Log(base 2) transform the ratios
  4. Normalize the log ratios on each microarray slide
  5. Normalize the log ratios for a set of slides in an experiment
  6. Perform statistical analysis on the log ratios
  7. Compare individual genes with known data
  8. Look for patterns (expression profiles; clusters) in the data (many programs are available to do this)
  9. Perform Gene Ontology term enrichment analysis (we will use MAPPFinder for this)
  10. Map onto biological pathways (we will use GenMAPP for this)

Individual Journal Assignment

  • Store this journal entry as "username Week 12" (i.e., this is the text to place between the square brackets when you link to this page).
  • Create the following set of links. These links should all be in your personal template; then use the template on your journal entry.
    • Link to your journal entry from your user page.
    • Link back from your journal entry to your user page.
    • Link to this assignment from your journal entry.
    • Don't forget to add the "BIOL368/F14" category to the end of your wiki page.

Begin Microarray Data Analysis

Getting to know your microarray data

The task for this week is to download and organize the microarray data corresponding to your paper to get it ready for analysis next week.

  1. Go to the ArrayExpress site for your data and download the following files:
    • "Investigation description" .idf.txt
    • "Sample and data relationship" .sdrf.txt
    • "Raw data" or .raw.gz
    • "Processed data" or .processed.gz
    • "Array design" .adf.txt
  2. Then upload these files to the OpenWetWare wiki (if possible) or to Lionshare and then link to them on your individual journal pages.
  3. From the methods section of your microarray paper, you need to figure out the following:
    • What samples did they collect and use for the microarray experiment?
    • How many microarray chips did they hybridize in the experiment?
    • Which samples were paired to hybridize on the chip?
    • Which was labeled red (Cy5)? Which was labeled green (Cy3)?
    • How many replicates did they perform of each type?
      • Biological replicates are made from entirely different biological samples.
      • Technical replicates are made when one biological sample is split at a particular stage in the procedure and then carried through to the end of the procedure.
  4. Record this information on your individual journal pages. If you have this from your journal outline, you can copy and paste it into your new journal page.
  5. Using the .sdrf.txt file, you need to then find the names of the files that correspond to the names of your samples from the paper. Make a list that says which file corresponds to which sample.
  6. The instructor will then show you which columns of data to copy into a new Master spreadsheet. You will upload this spreadsheet to the wiki and then link to it from your journal page.
  7. If you finish this assignment early, let the instructor know. I will then guide you in the next steps of the data analysis.

Shared Journal Assignment

  • Store your journal entry in the shared BIOL368/F14:Class Journal Week 12 page. If this page does not exist yet, go ahead and create it.
  • Link to the shared journal entry from your user page; this should be part of your template.
  • Link the shared journal page to this assignment page.
  • Sign your portion of the journal with the standard wiki signature shortcut (~~~~).
  • Add the "BIOL368/F14" category to the end of the wiki page (if someone has not already done so).



  • Answer the following questions:
    • Were you aware of this case of research fraud before viewing this video?
    • What are your initial reactions to hearing about this case?
    • What role did data sharing play in uncovering this fraud?
    • What additional information would you like to know about this case? (We will be visiting it again in subsequent weeks in the course.)
  • Please feel free to respond or comment on your classmates' reflections.