Integrative Biology 200A University of California, Berkeley "PRINCIPLES OF PHYLOGENETICS" Spring 2006 Alignment Lab In this lab we’re going to try to look at the effects of different methods of DNA alignment. We’ll try different settings in ClustalW. We’ll go through how to convert the output from ClustalW to a Nexus file, and how to manipulate that Nexus file. We’ll also use POY, which does alignment and tree searching together. Get the sequences Since a lot of you have not finished the Alignment Assignment, I’ve made this lab flexible depending on where you are. If you have not finished the alignment assignment, go to http://ib.berkeley.edu/courses/ib200a/Alignment%20Assignment.html and complete the assignment. Just skip the section on ClustalW in this lab. Instead do the alignments on line. Then start with the Making Nexus Files section, which will give you more complete instructions on how to convert to Nexus files and run them in PAUP* and continue from there. Use the Conus sequence file for all the parts of this lab. Incidentally I’ve modified this file, so you now read sequence names instead of accession numbers. The rest of you have three options: 1) If you want you can get sequences from the organism that you will be working on for your project. Go to http://www.ncbi.nlm.nih.gov/ search for your organism in the nucleotide data base, and try to find about fifteen sequences of a gene from different organisms that will be useful for your study. Download them to your desktop in FASTA format. 2)If you already know that there is nothing good on genbank (or you’re just in a rush), I’ve prepared an example FASTA file of COI sequences from about 1f Cephalopod species that you can download from http://ib.berkeley.edu/courses/ib200a/cephalopod_COI.txt. 3) For the really lazy you can just download the Conus sequence file from http://ib.berkeley.edu/courses/ib200a/sequences.fasta. I won’t hold it against you, and as I said above I’ve modified this file so that it’s prettier. ClustalW ClustalW is the most commonly used program for multiple sequence alignments. It works by first doing pairwise alignments of each pair of sequences to calculate distances between them. It uses those distances to derive a tree. That tree then guides the production of the multiple sequence alignment.You’ve already had a chance to use ClustalW a couple of times. The first time was through the Jalview sequence editor and the second time was through the Kyoto University Bioinformatics Center website. This time we’re going to go directly through the ClustalW web page of the European Bioinformatics Institute, where you have more control over the search parameters. Since ClustalW is the industry standard, we’re going to use it for comparison to POY, and to see the effects that parameters can have on the alignment. -Go to http://www.ebi.ac.uk/clustalw/#. For the first pass let’s just use the defaults. -From the output format menu select ‘aln wo/numbers’. Hit the Browse button and select your FASTA file. Then hit run. A web page will come up, letting you know that your job is in progress. It will automatically refresh, so that when your job is finished, a new web page will come up. -Pay attention to how long it takes, and when the job is finished, make a note of the alignment score. There will be four files available for you to download. The output file is a description of the alignment process. The .aln file is your actual sequence alignment in Clustal format. The .dnd file is the guide tree used to make the alignment. The input file is the file that you uploaded to ClustalW. -Download the alignment and guide tree files and give them unique names. -Repeat the same alignment only this time run a ‘fast’ rather than a ‘full’ alignment. Don’t forget to select ‘aln wo/numbers’. It probably won’t make a difference for this alignment, because you don’t have a very big matrix, but for more species or a longer sequence a fast alignment can lead to a big savings in time. The ‘fast’ alignment works by only considering a chunk of the sequence at a time. The options on the second line refer only to the ‘fast’ alignment and have to do with how big a chunk of the sequence you consider. How long did it take? Did it seam faster to you? Is your alignment score as good as it was last time? -Save the alignment file again, but don’t bother with the guide tree. Let’s do this one more time, but this time let’s give it really unrealistic parameters to see how the parameters do effect the alignment.-Set the gap open penalty to 1 and the gap extension penalty to 5. This will make it easier to start a gap then to extend it, a highly unrealistic situation. -Run the same sequences and save the alignment file. Don’t forget to select ‘aln wo/numbers’. Making Nexus Files In the next stage we are going to use Mesquite and PAUP* to make Nexus files and trees out of your alignment files. I haven’t introduced you to Mesquite yet, and we’ll deal with it more in a future lab. It is really good for this type of matrix conversion, so I’m just going to introduce you to some of the real basics here. -Open Mesquite: Applications>IB200>Mesquite Folder>Mesquite OSX -Open Your First Alignment: File>Open File -Navigate to your first alignment file, select it and hit open -An ‘Import File’ window will pop up, where you can select the format of the file you are inputting. Select Clustal (DNA/RNA) and hit OK -Now a ‘Save Inport File as Nexus File’ widow will pop up. Mesquite will automatically save any matrix you import as a Nexus File. You should give it a different name so that it won’t overwrite your original alignment file. I’m just changing ‘.txt’ to ‘.nex’. Hit Save. -That’s it. A nexus file with your aligned matrix should now appear in your original folder and a window should appear showing that same matrix. -Now open the other alignment files. You can open the other alignments in Mesquite without closing this one, so that you can look at all of them at once. -Scan over the alignments to compare them. Are they all the same? How is the third alignment with the bad parameters? Does it make sense, when compared to the other two? Deriving Trees -Now shut down Mesquite and open PAUP* (it’s in the same folder as all the rest). -Open the Nexus file from your first alignment.
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