Final answer:
A variation of more than 3% in the 16S rRNA gene sequence indicates significant genetic divergence, reflecting evolutionary relationships and genetic similarities between organisms. Option b is correct.
Step-by-step explanation:
A species that shows a variation of more than 3% in its 16S rRNA gene sequence compared to all other sequences indicates significant genetic divergence. This gene is often used in phylogenetics to study the evolutionary relationships between organisms because of its slow mutation rate and its presence in almost all bacteria. Variations in this gene sequence are the foundation for inferring genetic relationships. For example:
- Genetically, species D and A would be more similar to one another than species A and B, and vice versa.
- There would be greater genetic similarity between species D and B than between species A and E.
- Species A and E would share more genetic similarities with each other than with species B and D, and vice versa.
The fact that DNA sequences are more similar in more closely related organisms is evidence of common ancestry. If we consider individual genetic maps in a given species, we might find that they are genetically similar but not identical, reflecting slight variations that occur over time. An example of the practical use of the 16S rRNA gene sequence includes determining the relatedness of ancient bacterial strains to modern ones, such as comparing sequences from the 14th century to modern strains of bacterium pestis.
The notion that all species share a genetic code points to a common ancestor in the deep past, highlighting the connectedness of life through evolutionary history. The genetic code and well conserved genes provide robust evidence for tracing evolutionary relationships between species, making them crucial for understanding biodiversity and the history of life on Earth.