genome annotation

Genome annotation is the process of adding labels to a bare DNA sequence, turning a meaningless string of letters into an interpreted map. A raw genome is like an unmarked manuscript; annotation marks where the genes start and stop, what they do, and where the regulatory features lie.

Annotation works on two levels. Structural annotation identifies the locations of features — protein-coding genes, exons and introns, RNA genes, promoters, and repeats. Functional annotation then attaches biological meaning, predicting what each gene's product does, often by comparing it to genes of known function in other organisms.

Annotation is a prediction, not a certainty, and it improves over time. Computer algorithms make their best guesses from sequence patterns and similarity to known genes, but errors creep in, especially for unusual or poorly studied organisms. Annotations are continually revised as new experimental evidence accumulates, so a genome's labels are best treated as a living, updatable resource.