Molecular Evolution Tutorial

Tutorial for BIOL 6210 (Applied Pylogentics)

2 min read

HYPHY stuff: all files need for this tutorial are here

Identification of pervasive positive selection in cone snail venom

1. Get the file Conus.01.fas * This is our translated alignment

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2. We will now do the FUBAR analysis * This is a site specific method for detecting selection at the amino acid level, helpful in arms race scenarios

3. Go to http://www.datamonkey.org/dataupload.php

**4. ** Select choose file, select Conus.01.fas * Then, press Upload

5. If your data is no bueno, this is where it will let you know * It accepts fasta alignments and nexus files * Also listed here should be information about the alignments * If all is well, press Proceed to the analysis menu

6. Under Method select FUBAR

7. For now leave everything else alone and just press Run * If you had a nexus file, you could specify your own tree in Newick format * For now we’ll just let it use a generated neighbor joining tree 😢

8. The results will look like the following This file is gone now

  • This is a heat map showing sites are under positive selection and negative selection

PAML stuff

Identification of positive seleciton in the serine/threonine-protein kinase gene family

  • In the evolution vertebrates, we would like to know if the branch leading to the Teleost fishes (genes A50 to A54)

You will need the following files

1. TF105351.Eut.3.phy
* this is the alignment file

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2. TF105351.Eut.3.53876.tree * this is the newick tree with the branch of interest selected

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3. TF105351.Eut.3.53876.ctl * CodeML configuration file for alternative model

4. TF105351.Eut.3.53876.fixed.ctl * CodeML configuration file for null model

Run the following commands

codeml TF105351.Eut.3.53876.ctl
codeml TF105351.Eut.3.53876.fixed.ctl

Analyze results

Get liklihood values

grep lnL TF105351.Eut.3.53876.mlc

lnL(ntime: 41  np: 46):  -4707.209701      +0.000000

Liklihood value for alternative model is -4707.209701

grep lnL TF105351.Eut.3.53876.fixed.mlc

lnL(ntime: 41  np: 45):  -4710.222252      +0.000000

Liklihood value for null model is -4710.222252

ΔLRT = 2×(lnL1 - lnL0) = 2×(-4707.209701 - (-4710.222252)) = 6.02578

The degree of freedom is 1 (np1 - np0 = 46 - 45). p-value = 0.01098 (under χ²) => significant.

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