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Question #45994
The Question
A researcher transforms a winter-variety crop plant (which strictly requires vernalization) using a disarmed Agrobacterium tumefaciens vector. A resulting transgenic line unexpectedly exhibits constitutive flowering without any prior exposure to low temperatures. Genomic analysis reveals a single T-DNA insertion causing insertional mutagenesis in the host's nuclear genome. Based on the principles of plant growth and gene regulation, which of the following is the most scientifically accurate explanation for this phenotype?
Options
- A.
The T-DNA insertion inactivated a flowering repressor gene, thereby mimicking the physiological de-repression normally achieved by prolonged cold exposure.
- B.
The T-DNA vector introduced genes for gibberellin biosynthesis, which chemically substituted the requirement for low-temperature signaling.
- C.
The T-DNA integrated into the host's phytochrome locus, altering photoperiodic perception and forcing early floral meristem differentiation.
- D.
The T-DNA insertion caused the overproduction of cytokinins via the ipt gene, which synergistically bypassed the vernalization requirement.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Evolutionary_Exception
Tackle problems where standard rules evolve or change based on specific environmental constraints.
Concepts Behind This Question
Vernalization Mechanism|Agrobacterium Tumefaciens Mechanism
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: This question requires synthesizing Biotechnology (insertional mutagenesis via T-DNA) with Plant Physiology (the mechanism of vernalization).
The core misconception tested is viewing vernalization purely as a 'stimulatory' process rather than a 'de-repression' mechanism.
The primary trap (Option B) exploits the NCERT fact that 'Gibberellins substitute for cold treatment,' banking on students failing to realize that Agrobacterium vectors do not transfer GA genes.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Plant Growth and Development - Class 11 |
| Concept | Vernalization Mechanism |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |