EMBOSS: cons

| cons

## Function

Create a consensus sequence from a multiple alignment

## Description

cons calculates a consensus sequence from a multiple sequence alignment. To obtain the consensus, the sequence weights and a scoring matrix are used to calculate a score for each amino acid residue or nucleotide at each position in the alignment. The highest scoring residue goes into the consensus sequence if the score is higher than a user-specified "plurality" value, otherwise, there is no consensus at that position.

## Algorithm

To obtain the consensus, the sequence weights and a scoring matrix are used to calculate a score at each position in the alignment as follows. The residue (or nucleotide) i in an alignment column, is compared to all other residues (j) in the same column. The score for i is the sum over all residues j (not i=j) of the score(ij)*weight(j), where score(ij) is taken from a nucleotide or protein scoring matrix (see -datafile qualifier) and the "weight(j)" is the weighting given to the sequence j, which is given in the alignment file.

The highest scoring type of residue is then found in the column. If the number of "positive matches" (see below) for this residue is greater than the "plurality value" (see below), then this residue is the consensus residue. Otherwise there is no consensus for that position and an 'n' (nucleotide sequence alignment) or an 'x' (protein sequence alignment) character is written to the consensus sequence.

The positive matches for a residue i are calculated as being the sum of the corresponding sequence weights for all the residues that increase the score of residue i (i.e. that have a positive score). The "plurality" qualifier sets the cut-off for the number of positive matches (weighted) below which there is no consensus.

## Usage

Here is a sample session with cons

    % cons
    Create a consensus sequence from a multiple alignment
    Input (aligned) sequence set: dna.msf
    output sequence [dna.fasta]: aligned.cons

Go to the input files for this example
Go to the output files for this example

## Command line arguments

       Standard (Mandatory) qualifiers:
      [-sequence]          seqset     File containing a sequence alignment.
      [-outseq]            seqout     [.] Sequence filename and
                                      optional format (output USA)

       Additional (Optional) qualifiers:
       -datafile           matrix     [EBLOSUM62 for protein, EDNAFULL for DNA]
                                      This is the scoring matrix file used when
                                      comparing sequences. By default it is the
                                      file 'EBLOSUM62' (for proteins) or the file
                                      'EDNAFULL' (for nucleic sequences). These
                                      files are found in the 'data' directory of
                                      the EMBOSS installation.
       -plurality          float      [Half the total sequence weighting] Set a
                                      cut-off for the number of positive matches
                                      below which there is no consensus. The
                                      default plurality is taken as half the total
                                      weight of all the sequences in the
                                      alignment. (Any numeric value)
       -identity           integer    [0] Provides the facility of setting the
                                      required number of identities at a site for
                                      it to give a consensus at that position.
                                      Therefore, if this is set to the number of
                                      sequences in the alignment only columns of
                                      identities contribute to the consensus.
                                      (Integer 0 or more)
       -setcase            float      [@( $(sequence.totweight) / 2)] Sets the
                                      threshold for the positive matches above
                                      which the consensus is is upper-case and
                                      below which the consensus is in lower-case.
                                      (Any numeric value)
       -name               string     Name of the consensus sequence (Any string
                                      is accepted)

       Advanced (Unprompted) qualifiers: (none)
       Associated qualifiers:

       "-sequence" associated qualifiers
       -sbegin1            integer    Start of each sequence to be used
       -send1              integer    End of each sequence to be used
       -sreverse1          boolean    Reverse (if DNA)
       -sask1              boolean    Ask for begin/end/reverse
       -snucleotide1       boolean    Sequence is nucleotide
       -sprotein1          boolean    Sequence is protein
       -slower1            boolean    Make lower case
       -supper1            boolean    Make upper case
       -sformat1           string     Input sequence format
       -sdbname1           string     Database name
       -sid1               string     Entryname
       -ufo1               string     UFO features
       -fformat1           string     Features format
       -fopenfile1         string     Features file name

       "-outseq" associated qualifiers
       -osformat2          string     Output seq format
       -osextension2       string     File name extension
       -osname2            string     Base file name
       -osdirectory2       string     Output directory
       -osdbname2          string     Database name to add
       -ossingle2          boolean    Separate file for each entry
       -oufo2              string     UFO features
       -offormat2          string     Features format
       -ofname2            string     Features file name
       -ofdirectory2       string     Output directory

       General qualifiers:
       -auto               boolean    Turn off prompts
       -stdout             boolean    Write first file to standard output
       -filter             boolean    Read first file from standard input, write
                                      first file to standard output
       -options            boolean    Prompt for standard and additional values
       -debug              boolean    Write debug output to program.dbg
       -verbose            boolean    Report some/full command line options
       -help               boolean    Report command line options. More
                                      information on associated and general
                                      qualifiers can be found with -help -verbose
       -warning            boolean    Report warnings
       -error              boolean    Report errors
       -fatal              boolean    Report fatal errors
       -die                boolean    Report dying program messages

Standard (Mandatory) qualifiers | Allowed values | Default
--- | --- | ---
[-sequence] (Parameter 1) | File containing a sequence alignment. | Readable set of sequences | Required
[-outseq] (Parameter 2) | Sequence filename and optional format (output USA) | Writeable sequence | <*>.format
Additional (Optional) qualifiers | Allowed values | Default
-datafile | This is the scoring matrix file used when comparing sequences. By default it is the file 'EBLOSUM62' (for proteins) or the file 'EDNAFULL' (for nucleic sequences). These files are found in the 'data' directory of the EMBOSS installation. | Comparison matrix file in EMBOSS data path | EBLOSUM62 for protein EDNAFULL for DNA
-plurality | Set a cut-off for the number of positive matches below which there is no consensus. The default plurality is taken as half the total weight of all the sequences in the alignment. | Any numeric value | Half the total sequence weighting
-identity | Provides the facility of setting the required number of identities at a site for it to give a consensus at that position. Therefore, if this is set to the number of sequences in the alignment only columns of identities contribute to the consensus. | Integer 0 or more | 0
-setcase | Sets the threshold for the positive matches above which the consensus is is upper-case and below which the consensus is in lower-case. | Any numeric value | @( $(sequence.totweight) / 2)
-name | Name of the consensus sequence | Any string is accepted | An empty string is accepted
Advanced (Unprompted) qualifiers | Allowed values | Default
(none)

## Input file format

The USA of a set of aligned sequences.

### Input files for usage example

### File: dna.msf

    !!NA_MULTIPLE_ALIGNMENT

     dna.msf  MSF: 120  Type: N  January 01, 1776  12:00  Check: 3196 ..

     Name: MSFM1          Len:   120  Check:  8587  Weight:  1.00
     Name: MSFM2          Len:   120  Check:  6178  Weight:  1.00
     Name: MSFM3          Len:   120  Check:  8431  Weight:  1.00

    //

            MSFM1  ACGTACGTAC GTACGTACGT ACGTACGTAC GTACGTACGT ACGTACGTAC
            MSFM2  ACGTACGTAC GTACGTACGT ....ACGTAC GTACGTACGT ACGTACGTAC
            MSFM3  ACGTACGTAC GTACGTACGT ACGTACGTAC GTACGTACGT CGTACGTACG

            MSFM1  GTACGTACGT ACGTACGTAC GTACGTACGT ACGTACGTAC GTACGTACGT
            MSFM2  GTACGTACGT ACGTACGTAC GTACGTACGT ACGTACGTAC GTACGTACGT
            MSFM3  TACGTACGTA CGTACGTACG TACGTACGTA ACGTACGTAC GTACGTACGT

            MSFM1  ACGTACGTAC GTACGTACGT
            MSFM2  ACGTACGTTG CAACGTACGT
            MSFM3  ACGTACGTAC GTACGTACGT

## Output file format

The output consists of a sequence file holding the consensus sequence.

### Output files for usage example

### File: aligned.cons

    >EMBOSS_001
    ACGTACGTACGTACGTACGTACGTACGTACGTACGTACGTACGTACGTACGTACGTACGT
    ACGTACGTACGTACGTACGTACGTACGTACGTACGTACGTACGTACGTACGTACGTACGT

## Data files

cons uses the standard set of scoring matrix data files in the EMBOSS data directory.

EMBOSS data files are distributed with the application and stored in the standard EMBOSS data directory, which is defined by the EMBOSS environment variable EMBOSS_DATA.

To see the available EMBOSS data files, run:

    % embossdata -showall

To fetch one of the data files (for example 'Exxx.dat') into your current directory for you to inspect or modify, run:

    % embossdata -fetch -file Exxx.dat

Users can provide their own data files in their own directories. Project specific files can be put in the current directory, or for tidier directory listings in a subdirectory called ".embossdata". Files for all EMBOSS runs can be put in the user's home directory, or again in a subdirectory called ".embossdata".

The directories are searched in the following order:

- . (your current directory)
- .embossdata (under your current directory)
- ~/ (your home directory)
- ~/.embossdata

## Notes

The "identity" qualifier provides an additional constrain to "plurality" when determining a consensus residue at an alignment site. "identity" sets the required number of identities at a site for it to be included in the consensus. If for example this is set to the number of sequences in the alignment, then only a site with the same residue in all sequences would be included in the consensus.

The "setcase" qualifier sets the threshold for the positive matches above which the consensus residue is given is upper-case and below which it is in lower-case.

## References

None.

## Warnings

None.

## Diagnostic Error Messages

None.

## Exit status

It always exits with status 0.

## Known bugs

None.

## See also

Program name | Description
--- | ---
consambig | Create an ambiguous consensus sequence from a multiple alignment
megamerger | Merge two large overlapping DNA sequences
merger | Merge two overlapping sequences

## Author(s)

Tim Carver (tcarver © rfcgr.mrc.ac.uk)
MRC Rosalind Franklin Centre for Genomics Research Wellcome Trust Genome Campus, Hinxton, Cambridge, CB10 1SB, UK

## History

## Target users

This program is intended to be used by everyone and everything, from naive users to embedded scripts.

## Comments

None