GTF (Gene Transfer Format) is a refinement to GFF that tightens the specification. The first eight GTF fields are the same as GFF. The group field has been expanded into a list of attributes. Each attribute consists of a type/value pair. Attributes must end in a semi-colon, and be separated from any following attribute by exactly one space.

The attribute list must begin with the two mandatory attributes:

- gene_id value - A globally unique identifier for the genomic source of the sequence.
- transcript_id value - A globally unique identifier for the predicted transcript.

Example:
Here is an example of the ninth field in a GTF data line:

`gene_id "Em:U62317.C22.6.mRNA"; transcript_id "Em:U62317.C22.6.mRNA"; exon_number 1`

The Genome Browser groups together GTF lines that have the same transcript_id value. It only looks at features of type exon and CDS.

For more information on this format, see http://mblab.wustl.edu/GTF2.html.

If you would like to obtain browser data in GTF format, please refer to Genes in gtf or gff format on the Wiki.