Question

Which one of the following organisms has been disarmed and used to deliver desirable genes into animal cells?

• A. Retroviruses
• B. Cyanobacteria
• C. Yeast
• D. Baculoviruses

Hint:

Comparison of Disarmed Vectors:
$\bullet$ Plants: Agrobacterium tumefaciens (Ti-plasmid).
$\bullet$ Animals: Retroviruses (convert normal animal cells to transgenic cells without pathogenesis).

Answer 1

The Correct Option is A

Concept:
Viruses with natural mechanisms for integrating their genetic material into host cells can be genetically engineered (disarmed) to serve as delivery vehicles (vectors) for therapeutic or desired genes in mammalian systems.

Step 1: Retroviruses as Animal Cloning Vectors:
In their wild form, retroviruses are RNA viruses that infect animal cells and integrate their reverse-transcribed viral DNA stably into the host cell chromosomes, sometimes transforming normal cells into cancerous cells.
In genetic engineering, the pathogenic and oncogenic genes of retroviruses are deleted or disarmed.
These disarmed retroviruses retain their efficient cell-entry and host-genome integration capabilities, making them optimal vectors for delivering functional therapeutic genes into animal cells (e.g., in gene therapy for ADA deficiency).

Step 2: Examining the Other Options:
- Cyanobacteria: Photosynthetic prokaryotes, not used as animal transformation vectors.
- Yeast: Eukaryotic unicellular organisms used as expression hosts or cloning hosts (e.g., YAC vectors), but not as delivery viruses.
- Baculoviruses: Pathogens belonging to the genus Nucleopolyhedrovirus that attack insects and other arthropods; used as biocontrol agents.

Step 3: Final Selection:
Therefore, disarmed Retroviruses are used to deliver desirable genes into animal cells.