167. Which one of the following conditions eliminates the possibility of horizontal gene transfer from a
transgenic plant?
1. Single copy nuclear events
2. Multicopy nuclear events
3. Plastid transformation events
4. Marker free events

Plastid Transformation and Its Role in Preventing Horizontal Gene Transfer

Genetically modified (transgenic) plants often raise concerns regarding horizontal gene transfer (HGT) — the movement of genes from plants to microorganisms in the environment. Understanding which strategies reduce or eliminate this risk is crucial in biosafety and regulatory assessments.

Which Condition Eliminates the Possibility of HGT?

Let’s analyze the options:

1. Single copy nuclear events

   • Still involve nuclear DNA which can potentially be transferred, although the risk is lower.

2. Multicopy nuclear events

   • Multiple copies increase the likelihood of gene expression and potential transfer, making this more prone to HGT.

3. Plastid transformation events

   • Correct. Plastids (such as chloroplasts) are maternally inherited in most plants and rarely found in pollen. This greatly reduces the likelihood of gene escape via pollen or environmental DNA uptake by microbes.

4. Marker free events

   • Although marker-free is good for food and regulatory acceptance, it doesn’t inherently eliminate HGT risk from nuclear DNA.

Why Plastid Transformation Is Safer

• Maternal Inheritance: Limits gene spread via pollen.

• Compartmentalization: Plastid DNA is isolated from the nuclear genome.

• Low Homology with Microbial DNA: Reduces chance of recombination with microbial genomes.

Correct Answer:

3. Plastid transformation events

This approach is a biosafe genetic engineering strategy that effectively minimizes the risk of horizontal gene transfer, making it the preferred method when environmental containment is a priority.