Nexus file

The extensible NEXUS file format is widely used in bioinformatics. It stores information about taxa, morphological and molecular characters, distances, genetic codes, assumptions, sets, trees, etc.[1] Several popular phylogenetic programs such as PAUP*,[2] MrBayes,[3] Mesquite,[4] MacClade[5] and SplitsTree[6] use this format.

Nexus format

Filename extensions	usually .nex or .nxs
Internet media type	application/octet-stream
Magic number	'#NEXUS\n'
Developed by	Maddison DR, Swofford DL, Maddison WP
Initial release	December 1997
Type of format	bioinformatics
Open format?	Yes

Syntax

A NEXUS file is made out of a fixed header #NEXUS followed by multiple blocks. Each block starts with BEGIN block_name; and ends with END;. The keywords are case-insensitive. Comments are enclosed inside square brackets [...].[7]

There are a few pre-defined block names for common types of data. Examples include:[7]

TAXA block

The TAXA block contains information about taxa.

DATA block

The DATA block contains the data matrix (e.g. sequence alignment).

TREES block

The TREES block contains phylogenetic trees described using the Newick format, e.g. ((A,B),C);:

The following example uses the three block types above:

#NEXUS
Begin TAXA;
  Dimensions ntax=4;
  TaxLabels SpaceDog SpaceCat SpaceOrc SpaceElf
End;

Begin data;
  Dimensions nchar=15;
  Format datatype=dna missing=? gap=- matchchar=.;
  Matrix
    [ When a position is a "matchchar", it means that it is the same as the first entry at the same position. ]
    SpaceDog   atgctagctagctcg
    SpaceCat   ......??...-.a.
    SpaceOrc   ...t.......-.g. [ same as atgttagctag-tgg ]
    SpaceElf   ...t.......-.a.           
  ;
End;

BEGIN TREES;
  Tree tree1 = (((SpaceDog,SpaceCat),SpaceOrc,SpaceElf);
END;

See also

• Newick format
• NeXML format
• phyloXML

References

1. Maddison DR, Swofford DL, Maddison WP (1997). "NEXUS: An extensible file format for systematic information". Systematic Biology. 46 (4): 590–621. doi:10.1093/sysbio/46.4.590. PMID 11975335.
2. PAUP* Archived 2006-09-03 at the Wayback Machine — Phylogenetic Analysis Using Parsimony *and other methods
3. MrBayes
4. Mesquite: A modular system for evolutionary analysis
5. MacClade
6. Huson and Bryant, Application of Phylogenetic Networks in Evolutionary Studies, Mol Biol Evol (2005) 23 (2): 254-267. https://doi.org/10.1093/molbev/msj030
7. Detailed NEXUS specification

External links

• NEXUS file format — detailed explanation with many examples
• NEXUS format — a good description of the format and its uses in the field
• Nexus to phyloXML converter
• NeXML
• Nexus to Fasta converter