Hepatitis B virus (HBV) genome type: Which nucleic acid form characterizes HBV?

Introduction:
HBV is the prototype of the Hepadnaviridae family, notable for its unusual genomic organization and reverse transcription step. Identifying its nucleic acid type is a fundamental virology fact.

Given Data / Assumptions:

• HBV virions contain a relaxed circular DNA genome with one complete and one incomplete strand.
• The replication cycle includes reverse transcription of an RNA intermediate inside nucleocapsids.
• We must choose the best descriptor of the incoming genome in virions.

Concept / Approach:
HBV packages a partially double-stranded DNA molecule. After infection, host repair completes the gap to form covalently closed circular DNA (cccDNA) in the nucleus. Although reverse transcription occurs during replication, the genome present in virions is DNA, not RNA.

Step-by-Step Solution:
Recall that HBV is a DNA virus with reverse transcription. Identify the virion genome as relaxed circular partially dsDNA. Select the option that explicitly states partially dsDNA for maximum precision.

Verification / Alternative check:
Electron microscopy and biochemical analyses confirm the gapped DNA structure, later repaired to cccDNA intracellularly.

Why Other Options Are Wrong:

• ssRNA / dsRNA / negative-sense RNA: Do not describe HBV; those apply to RNA virus families.
• ssDNA: Not the HBV genome state in virions.

Common Pitfalls:
Confusing the use of reverse transcriptase with being an RNA virus; HBV is a DNA virus with a unique replication strategy.

Final Answer:
HBV contains partially double-stranded DNA in virions.