Which Molecular Markers Cannot Establish Phylogenetic Relationships? Understanding the Limits of tRNA Sequencing

Establishing phylogenetic relationships among organisms is a cornerstone of evolutionary biology. Molecular markers such as ribosomal RNA genes and mitochondrial DNA have revolutionized the field, allowing scientists to reconstruct evolutionary trees with high precision. However, not all molecular sequences are equally useful for this purpose. Among the commonly discussed options—5S rRNA, tRNA sequencing, 16S rRNA, and mitochondrial DNA—one stands out as unsuitable for robust phylogenetic analysis: tRNA sequencing.

The Role of Molecular Markers in Phylogenetics

Phylogenetic studies rely on molecular sequences that are:

• Conserved enough to be found across a wide range of organisms,

• Variable enough to reflect evolutionary divergence.

Let’s examine each marker in the context of phylogenetic utility:

1. 5S rRNA

• 5S ribosomal RNA is a component of the ribosome and is present in all domains of life.

• Its sequence is conserved but contains enough variation to be useful in certain phylogenetic studies, especially at higher taxonomic levels.

2. 16S rRNA

• 16S rRNA is a gold standard for phylogenetic studies in prokaryotes and is widely used to resolve relationships from species to higher taxonomic levels.

• Its variable and conserved regions make it ideal for constructing evolutionary trees1.

3. Mitochondrial DNA

• Mitochondrial DNA (mtDNA) evolves relatively quickly and is maternally inherited, making it valuable for studying relationships at the species, genus, and sometimes family levels136.

• Complete mtDNA or specific mitochondrial genes are commonly used for phylogenetic reconstruction in animals and plants.

4. tRNA Sequencing

• tRNA genes are highly conserved in both sequence and structure because of their essential role in translation.

• The high conservation and short length of tRNA genes mean they provide very little phylogenetic signal and cannot resolve evolutionary relationships effectively.

• tRNA sequencing is not used for establishing phylogenetic relationships, as it lacks the necessary variability and phylogenetic information.

Scientific Consensus

Current research and practical experience confirm that tRNA sequences do not provide sufficient variability or resolution for phylogenetic studies. In contrast, 5S rRNA, 16S rRNA, and mitochondrial DNA are established and effective tools for reconstructing evolutionary histories16.

Conclusion

Phylogenetic relationships among organisms cannot be established on the basis of tRNA sequencing. For robust and informative evolutionary analysis, scientists rely on markers like 16S rRNA, 5S rRNA, and mitochondrial DNA.

Correct answer:
(2) t-RNA sequencing