In the context of viral structure, the genetic material of a virus consists of which of the following?

• A. Only single-stranded DNA
• B. Only double-stranded RNA
• C. Both DNA and RNA always present together
• D. Either DNA or RNA (but not both in the same virion)

Answer: (D)

Verified step by step guidance

1. Understand that viruses contain genetic material that can be either DNA or RNA, but not both simultaneously within the same viral particle (virion).
2. Recall that viral genomes vary widely: some viruses have single-stranded DNA (ssDNA), others have double-stranded DNA (dsDNA), some have single-stranded RNA (ssRNA), and others have double-stranded RNA (dsRNA).
3. Recognize that the viral genome type is a key classification criterion for viruses and influences their replication strategy.
4. Note that the options 'Only single-stranded DNA' or 'Only double-stranded RNA' are too restrictive because viruses can have different types of nucleic acids, not limited to just one form.
5. Conclude that the correct understanding is that a virus contains either DNA or RNA as its genetic material, but never both together in the same virion.