...
Often, the first thing you (or your boss) want to know about your sequencing run is simply, "how many reads are there?". For the $BI/gva_course/mapping/data/SRR030257_1.fastq file, the answer is 3,800,180. How can we figure that out?
The grep (or Global Regular Expression Print) command can be used to determine the number of lines which match some criteria as shown above. Above we used it to search for:
- anything from the group of ACTGN with the [] marking them as a group
- matching any number of times *
- from the beginning of the line ^
- to the end of the line $
Here, since we are only interested in the number of reads that we have, we can make use of knowing the 3rd line in the fastq file is a + and a + only, and grep's -c option to simply report the number of reads in a file.
| Code Block |
|---|
| language | bash |
|---|
| title | Can you use the information above to write a grep command to count the number of reads in the same file? |
|---|
| collapse | true |
|---|
|
grep -c "^+$" $BI/gva_course/mapping/data/SRR030257_1.fastq
|
...
You may recall from today's first tutorial, that we used the conda system to install fastqc in preparation for this tutorial. If you did not complete that, please go back and do so now, and don't hesitate to ask a question if you are having difficulties. Interactive GUI versions are also available for Windows and Macintosh and can be downloaded from the Babraham Bioinformatics web site. We don't want to clutter up our work space so copy the SRR030257_1.fastq file to a new directory named GVA_fastqc_tutorial on scratch, and use fastqc's help option after it is installed to figure out how to run the program. Once the program is completed use scp to copy the important file back to your local machine (The bold words are key words that may give you a hint of what steps to take next)
| Code Block |
|---|
| language | bash |
|---|
| title | Running FastQC example |
|---|
| collapse | true |
|---|
|
mkdir $SCRATCH/GVA_fastqc_tutorial
cd $SCRATCH/GVA_fastqc_tutorial
cp $BI/gva_course/mapping/data/SRR030257_1.fastq .
fastqc -h # examine program options
fastqc SRR030257_1.fastq # run the program |
| Note |
|---|
| title | Potential error with fastqc program execution |
|---|
|
As noted during Monday's class, several people were experiencing an that included text:
| No Format |
|---|
Can't locate warnings.pm: /corral-repl/utexas/BioITeam//local/share/perl5/warnings.pm: Permission denied at /home1/08965/vramirez/miniconda3/envs/fastqc-test/bin/fastqc line 2.
BEGIN failed--compilation aborted at /home1/08965/vramirez/miniconda3/envs/fastqc-test/bin/fastqc line 2. |
This is believed to be related to the occasional "permission is denied" error some were getting when trying to access the BioITeam contents. If you have circled back to this, and are experiencing this error please get my attention. I have been unable to troubleshoot this fully as I have not been having the problem, but I believe the answer will be found in: | Code Block |
|---|
| language | bash |
|---|
| title | commands for troubleshooting fastqc error |
|---|
| perl -V #bottom @INC: section
perldoc -l warnings # should list the specific version of the warnings module attempted to be being used
echo $PERL5LIB |
Solution will likely be modifying $PERL5LIB away from BioITeam contents which should force conda environment versions.
|
| Expand |
|---|
| title | What results did you get from your FastQC analysis? |
|---|
|
| No Format |
|---|
| title | ls -l shows something like this |
|---|
| -rwxr-xr-x 1 ded G-802740 498588268 Jun 13 12:06 SRR030257_1.fastq
-rw-r--r-- 1 ded G-802740 291714 Jun 13 12:07 SRR030257_1_fastqc.html
-rw-r--r-- 1 ded G-802740 455677 Jun 13 12:07 SRR030257_1_fastqc.zip |
The SRR030257_1.fastq file is what we analyzed, so FastQC created the other two items. SRR030257_1_fastqc.html represents the results in a file viewable in a web browser. SRR030257_1_fastqc.zip is just a Zipped (compressed) version of the results. |
...