Endosymbiotic theory evidence: What major evolutionary inference is supported by the genomic sequence of the obligate intracellular parasite Rickettsia prowazekii?

Introduction / Context:
Endosymbiotic theory proposes that mitochondria originated from an alphaproteobacterial ancestor that took up residence inside a proto-eukaryotic cell. Comparative genomics of intracellular bacteria has provided strong evidence for this evolutionary event.

Given Data / Assumptions:

• Rickettsia prowazekii is an obligate intracellular alphaproteobacterium.
• Its genome shows similarities to mitochondrial genes and organization.
• We identify the evolutionary conclusion best supported by such data.

Concept / Approach:

Sequence homology, shared metabolic pathways, and similarities in replication/translation systems between Rickettsia and mitochondria indicate common ancestry. Reductive evolution of intracellular bacteria mirrors the reduced gene content of mitochondria, further supporting endosymbiosis.

Step-by-Step Solution:

Verification / Alternative check:

Multiple independent analyses (gene trees, membrane features, translation components) converge on the endosymbiotic origin.

Why Other Options Are Wrong:

Large genomes: Rickettsia genomes are reduced, not large.

Similarity to viruses: bacteria and viruses differ fundamentally; sequence data do not support a viral-like genome.

“All bacteria from viruses”: unsupported and contrary to evolutionary evidence.

Common Pitfalls:

Assuming any intracellular parasite is a direct mitochondrial ancestor; the inference is about lineage and shared ancestry, not direct descent from modern Rickettsia.

Final Answer:

Mitochondria evolved from endosymbiotic bacteria