Genome Annotation
One-Sentence Definition
Genome annotation locates genes and other features on an assembled genome and assigns predicted functions to them.
Simple Explanation
After assembling the DNA, annotation writes the labels: “here is a gene, and it probably makes a β-lactamase.”
Detailed Scientific Explanation
Two layers:
- Structural — find CDS, rRNA, tRNA, ncRNA, CRISPR arrays (Prodigal, Barrnap, tRNAscan)
- Functional — assign names/ontologies by homology or profiles (BLAST/DIAMOND, HMMER + Pfam, KEGG, COG, GO)
Common bacterial pipelines: Prokka, Bakta, PGAP (NCBI).
Caveats:
- Function transferred by homology is a hypothesis, not proof
- “Hypothetical protein” is very common in non-model organisms
- Annotation version changes downstream gene counts and pangenome results
Mechanism
Gene prediction models (Markov models trained on coding statistics) + alignment/profile search against curated reference sets.
Clinical Importance
- Virulence and resistance genes come out of this step for reporting (AMR Gene Databases, Virulence Factor Databases)
Research Importance
- Basis of Comparative Genomics and Pangenome Analysis
Diagnostic Relevance
- Structured input for clinical genomics reports
AMR Relevance
- Correct CDS boundaries matter for detecting truncations (e.g., porin loss → resistance)
Related MOCs
Active Recall Questions
- Structural vs functional annotation?
- Why is homology-based function a hypothesis?
- Which resistance mechanism shows up as a truncated gene?
Connections
- Genome Assembly → annotation → Pangenome Analysis · Sequence Alignment and BLAST