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Ensembl supplies FASTA formatted files for genome sequence and GFF formatted files for the annotation The following provides a simple scheme to produce the correctly formatted files for SyMAP.

Download
Convert files
   xToSymap Ensembl Options
   Scaffolds
            
General
   Load files into SyMAP
   Editing the script
   What the ConvertEnsembl script does

Reasons to convert files

  1. Only chromosome and optional scaffold sequences are processed.
  2. Only the 'protein-coding' genes are processed.
  3. Gene attributes:
    ID From the input gene attributes.
    Name From the input gene attributes (if it is not equal ID).
    desc Is the gene description, where symbols (e.g. %3B) are replaced with the correct character.
    It removes the ending "[Source:..." from the input description.
    rnaID Is equal to the first mRNA ID. Following the ID is (n), where n=number of mRNAs for the gene.
    proteinID (optional) Is equal the 1st CDS protein-id of the 1st mRNA.
If there are problems converting the Ensembl file(s), then symap will have problems loading the original Ensembl files. Ensembl formats can be inconsistent, so this may not take everything into account; check your files with the xToSymap Summarize function. See Tested genomes and editing the script.

Download

The following instructions were updated on 21-Jan-2026.
  1. Go to Ensembl. For plants and fungi, go to EnsemblPlant and EnsemblFungi, respectively.
  1. Select your species from the Select a species drop-down under All genomes, as shown on the right.
    This will go to your species webpage with the Genome assembly and Gene annotation, as illustrated in the image below.

  2. Select Download DNA sequence (FASTA).
    This takes you to a FTP site. It is recommended that you download the [prefix].dna_sm.toplevel.fa.gz, as it is the soft masked chromosome sequences.

  3. Select the GFF3 from the Download genes, cDNAs, ncRNA, proteins - FASTA - GFF3 line.
    This takes you to an FTP site. Download the [prefix].gff3.gz file.
Select

Convert files

xToSymap Ensembl Options Scaffolds Go to top
  1. Go to the symap_5/data/seq directory.
  2. Make a subdirectory for your species (see Project directory) and move the FASTA and GFF files into the directory.
  3. Start the xToSymap program.
    • Select the appropriate xToSymap Ensembl options (described below).
    • Then select Convert.
The program will output statistics to the terminal and a log file. The cabbE directory will contain the following: 

data/seq/cabbE/
      Brassica_oleracea.BOL.59.gff3.gz
      Brassica_oleracea.BOL.dna_sm.toplevel.fa.gz
      annotation/
         anno.gff
         gaps.gff
      sequence/
         genomic.fna

xToSymap Ensembl Options

The FASTA file must end in ".fa" and the annotation file must end in ".gff3" (the Ensembl defaults). They may be zipped, i.e. have a '.gz' suffix.
OptionDescriptionDefault
Only #,X,Y,I2 Most Ensembl FASTA header lines specify the chromosome number, X, Y or Roman numeral. Only these sequences will be written. Any that have 'chromosome' on their header line.
Scaffolds1Any sequence with 'scaffold' in the header line will be written to the FASTA file. See ScaffoldsChromosomes only
Mt/Pt Mt/Pt chromosomes will be included in FASTA and GFF. Only the first occurrence will be included. No Mt/Pt
Only prefix2Only sequences with the specified prefix will be processed. None
Protein-id A new attribute called proteinID= will have the value of the protein-id of the 1st CDS for the 1st mRNA of the gene. This can be searched using the viewSymap Queries. Do not include
VerbosePrint extra information, e.g. see verbose log No extra information

1You may include Scaffolds, and then limit the input on the symap Load by setting
  Minimal length in the project's Parameters.

2For situations needing Only #,X,Y,I and Only prefix, see exceptions. This mainly occur if the words 'chromosome' or 'scaffold' are not in the header lines.

Rules: There are variations in the text associated with >seqid header lines. The rules used by this script are as follows:

  1. If Only prefix is not blank, sequences are filtered out if the seqid does not start with the prefix. Then the following rules 2-4 are applied to the non-filtered sequences:
     
  2. Chromosomes: A sequence is considered a chromosome if: (a) the ">" is followed by a number, X, Y, or roman numeral, or (b) the header line contains the word 'chromosome'.
    • The exception is when the header line starts with '>Mt' or '>Pt', these will not be output unless Mt/Pt is selected.
    • Chromosomes are always output unless Only prefix is set, and the prefix does not match.
    • >seqid: If the ">" line contains 'chromosome N', where N={number, X, Y or roman numeral}, than this number is used. Otherwise, the word following 'chromosome' is used (e.g. C1). For example,
         >C1 dna_sm:chromosome chromosome:BOL:C1:1:43764888:1 REF
      is replaced with
         >C1 C1 chromosome

  3. Scaffolds: A sequence is considered a scaffold if the header line contains the word 'scaffold'.
    • They will only be output if Scaffolds is selected.
    • >seqid: 'Scaf' followed by a consecutive number.

  4. Unknown: All other ">" entries are considered 'unknown'.
    • They will only be output if Only prefix matches the input header line seqid.
    • >seqid: 'Unk' followed by a consecutive number.
See Summarize to help determine how to set the options for your input.

Scaffolds

By default, the Convert option creates the genomic.fna file with only the chromosomes. However, you can have it also include the scaffolds by selecting Scaffolds. This will include all chromosomes and scaffolds in the genomic.fna file, where they will be prefixed 'C' and 's', respectively. Beware, there can be many tiny scaffolds. If they all aligned in SyMAP, it causes the display to be very cluttered. Hence, it is best to just align the largest ones (e.g. the longest 30); merge them if possible, then try the smaller ones. You should set the following SyMAP project's Parameters:
  1. Group prefix needs to be blank as there is no common prefix now.
  2. Minimum length should be set to only load the largest scaffolds.
    Calculate the length using the xToSymap Lengths.

General

Load files into SyMAP Editing the script What the ConvertEnsembl script does Go to top

Load files into SyMAP

The above scenario puts the files in the default SyMAP directories.
  1. When you start up ./symap, you will see your projects listed on the left of the panel (e.g demos).
  2. Check the projects you want to load, which will cause them to be shown on the right of the symap panel.
  3. For the project you want to load, open the Project Parameters panel to enter the appropriate values.
  4. Then select Load Project.

Editing the ConvertEnsembl script

The script scripts/ConvertEnsembl.java executes the same code as the xToSymap Ensembl Convert. The Ensembl files are not consistent in their header lines. Hence, the parsing could be incorrect. If it is not parsing correctly (the summary output should indicate if it is correct or not), edit the program as described here.

What the ConvertEnsembl script does

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FASTA: Reads the file ending in '.fa.gz' and writes a new file called sequence/genomic.fna with the following changes:
  1. Sequences are output according to the option Rules.
  2. Gaps of >30,000 are written to the annotation/gap.gff file (this value can be changed in the xToSymap interface).

GFF: Reads the file ending in 'gff3.gz' and writes the file annotation/anno.gff. The gff3 format has 9 columns, where the first is the 'seqid', the third is the 'type' (e.g. feature 'gene'), the last column is a semicolon-delimited keyword=value 'attribute' list. The file is processed as follows:
  1. Only lines with the 'type' (3rd column) equal 'gene', 'mRNA' and 'exon' are read.
  2. Genes with "biotype=protein_coding" are written to file, followed by the first mRNA and its exons.
  3. All lines have their seqID replaced with the assigned seqID used in the FASTA file. They all have a modified set of attributes written.
  4. The only gene attributes retained are ID, description and Name (if it is not the same as ID). It removes the ending "[Source:..." from the input description.
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