Phage architecture — Which capsid symmetry is exhibited by most bacteriophages (tailed phages)?

Introduction / Context:
Bacteriophages display diverse virion structures. The majority of well-studied phages that infect bacteria are the tailed Caudoviricetes, whose overall virion organization is considered “complex.”

Given Data / Assumptions:

• Tailed phages possess an icosahedral head plus a helical tail and baseplate/tail fibers.
• Symmetry classification considers the entire virion, not just the head.
• Non-tailed phages exist but are less common in classical teaching sets.

Concept / Approach:
Because tailed phages combine distinct symmetrical components (icosahedral head and helical tail), the composite virion is classified as having complex symmetry. Hence “Complex” best describes most phages overall, despite the icosahedral symmetry of their heads alone.

Step-by-Step Solution:

Verification / Alternative check:
Electron micrographs of T-even phages and lambda phage illustrate the complex assembly.

Why Other Options Are Wrong:

• Helical or icosahedral alone do not describe the combined structure.
• “None of these” ignores the well-accepted “complex” category.

Common Pitfalls:
Focusing solely on head symmetry; consider the entire virion.

Final Answer:
Complex