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Question #45901
The Question
A wild-type cry gene from Bacillus thuringiensis is introduced into a transgenic crop. Although the mRNA is transcribed efficiently, the plant exhibits negligible insect resistance. Biochemical analysis reveals the presence of abnormally short, misfolded Cry polypeptides. Which of the following statements correctly identifies the genetic principle responsible for this failure and the subsequent physiological step that is disrupted?
Options
- A.
The plant's RNA polymerase cannot recognize bacterial promoters, preventing the synthesis of the protoxin required for pore formation in the insect midgut.
- B.
Differences in codon usage bias between the bacterium and the plant caused translational stalling, yielding a defective protoxin that cannot be solubilized by the alkaline pH of the insect midgut.
- C.
The degeneracy of the genetic code led to alternative splicing of the cry mRNA in the plant, producing a toxin that is neutralized by the acidic pH of the insect gut.
- D.
The plant lacks the specific alkaline proteases necessary to convert the inactive protoxin into the active toxin prior to ingestion by the insect.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Bt Toxin Activation Trigger|Genetic Code Degeneracy|Transgenic Animal Purpose
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: This question integrates Biotechnology (Bt toxin activation) with the Molecular Basis of Inheritance (Genetic code degeneracy and translation).
The primary misconception tested is the location of toxin activation (insect gut vs. plant) and the physiological trigger (alkaline vs. acidic pH), combined with the advanced application of why heterologous gene expression often fails without codon optimization.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Molecular Basis of Inheritance - Class 12 |
| Concept | Genetic Code Degeneracy |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |