Practice question

The small subunit 16S rRNA gene serves as a universal molecular chronometer for bacteria due to its ubiquitous presence, essential function, and mosaic of conserved and hypervariable regions. Approximately 1500 nucleotides allow robust placement into phyla, classes, orders, families, and genera using database comparisons and phylogenetic trees. Its slow evolution provides reliable broad classification and microbiome profiling for uncultured organisms. However high sequence conservation among close relatives restricts discriminatory power at species and strain levels, necessitating multilocus sequence typing or whole-genome approaches for finer resolution.