Annotation Extension

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 Note that this documentation is being reviewed 


Other pages to review

TO DO Review/update

Introduction

Each GO annotation pairs a single gene product identifier to a single term from the ontology. This format is very powerful however it can also restrict the descriptiveness of a specific instance of a functioning or subcellular location; there must be a pre-existing term in the ontology that provides full details of the specific aspects of the function.

It is not always possible to create individual terms that precisely describe the context of each activity (e.g. the cellular or anatomical location, the dependency on other processes, or particular, specific protein targets).

It is less restrictive if the annotator is able to combine additional terms in a single annotation to provide a more detailed functional description for an individual gene product.

This page describes the Annotation Extension field (column 16) in the Gene Association File GAF2.0 file format, which allows GO terms to be further specified, using gene product or chemical identifiers or terms from GO or external OBO ontologies.

When an annotator chooses to do this, they are effectively creating "on-the-fly" cross-product term. We say "on-the-fly" because the combinatorial term is not added to the ontology (although it could be at a later stage, if the ontology editors choose to create the appropriate GO term).