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Question #46462
The Question
A population of cotton bollworms feeding continuously on transgenic Bt cotton develops field resistance over several generations. Upon ingestion by the resistant insects, the Cry protoxin is successfully solubilized and proteolytically cleaved in the gut, yet it fails to cause midgut epithelial cell lysis. Which of the following best explains the molecular mechanism of this resistance and the type of natural selection operating on the population?
Options
- A.
Mutation in midgut epithelial receptors preventing active toxin binding; Directional selection.
- B.
Shift in midgut pH to an acidic range preventing protoxin solubilization; Directional selection.
- C.
Integration of the cry gene into the insect genome to produce antitoxins; Disruptive selection.
- D.
Mutation in midgut epithelial receptors preventing active toxin binding; Stabilizing selection.
Check Your Answer
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
Alkaline pH|Cry Gene|Lepidopteran Midgut
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: This question tests the synthesis of Biotechnology (Mechanism of Cry proteins) and Evolution (Types of Natural Selection).
The primary trap is the 'Reading Comprehension Trap'—students who reflexively associate Bt resistance with 'lack of alkaline pH' will choose Option B, ignoring the premise that solubilization and cleavage have already occurred.
It also requires distinguishing Directional selection (shifting towards resistance) from Stabilizing selection.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Evolution - Class 12 |
| Concept | Natural Selection Directionality |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |