Capsid symmetry identification: which common human viruses are typically icosahedral? Choose the most accurate statement about capsid symmetry for polioviruses and adenoviruses.

Introduction / Context:
Recognizing capsid symmetry is a core skill in general virology. Many non-enveloped viruses possess icosahedral capsids that confer robustness and efficient genome packaging. This question asks you to match two familiar human viruses with their typical symmetry class.

Given Data / Assumptions:

• Poliovirus is a non-enveloped, positive-sense RNA virus (Picornaviridae).
• Adenovirus is a non-enveloped, double-stranded DNA virus (Adenoviridae).
• Icosahedral symmetry is common among non-enveloped human viruses.

Concept / Approach:
Polioviruses have small, T=3 icosahedral capsids composed of VP1–VP4 proteins. Adenoviruses have larger icosahedral capsids with characteristic fiber projections at the vertices. Despite differences in size and composition, both share icosahedral symmetry.

Step-by-Step Solution:
Recall poliovirus as a classic icosahedral picornavirus.Recall adenovirus particle with icosahedral geometry and vertex fibers.Select the statement affirming that both are icosahedral.

Verification / Alternative check:
Electron micrographs and structural studies consistently show icosahedral geometry for both viruses, confirming the match.

Why Other Options Are Wrong:
Claims that one or both are helical or lack defined symmetry contradict standard structural virology. Helical symmetry is typical of many enveloped RNA viruses (for example, orthomyxoviruses), not these two.

Common Pitfalls:
Confusing adenoviral vertex fibers with a non-icosahedral structure. The fibers decorate, but do not change, the underlying icosahedral symmetry.

Final Answer:
Both polioviruses and adenoviruses generally exhibit icosahedral capsid symmetry.