Question

Given below are two statements: 
• [Statement (I):] Viruses can insert their genes into the host genome. 
• [Statement (II):] Viral gene insertion in nature may lead to major phenotypic alteration in the host. 
In light of the above statements, choose the most appropriate answer from the options given below. 
 

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Integrated viral sequences in host genomes are called endogenous viruses.
In plants, these sequences can remain dormant for generations until environmental stresses (such as extreme temperatures) trigger them to become active.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Viruses are obligate intracellular parasites that must hijack host cellular machinery to replicate.
Some viruses have life cycles that involve integrating their viral genome into the DNA of the host cell.

Step 3: Detailed Explanation:
Let us evaluate the two statements:
- Statement (I) is correct: Many viruses can integrate their genetic material into the host genome.
In animal systems, retroviruses (like HIV) use reverse transcriptase to convert their RNA into DNA, which is then integrated into the host genome.
In plant systems, certain double-stranded DNA viruses, such as pararetroviruses (e.g., Banana streak virus), can integrate into the host plant's genomic DNA.
These integrated viral sequences are known as endogenous viral elements (EVEs).
- Statement (II) is correct: The insertion of viral genes into the host genome can disrupt host genes or alter their expression patterns.
This insertion can cause phenotypic changes in the host.
In animals, integration near cellular proto-oncogenes can lead to cancer.
In plants, environmental stress can trigger the integrated viral DNA to excise and express active viral particles, causing disease symptoms such as leaf streaking and stunted growth.
Therefore, both statements are correct.

Step 4: Final Answer:
Both Statement (I) and Statement (II) are correct, matching Option (A).