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Question #46473
The Question
In certain vertebrates, researchers studying the evolutionary developmental biology of vestigial organs discovered that the structural genes coding for these ancestral traits remain completely intact in the genome, lacking any frameshift or nonsense mutations. However, their phenotypic expression is completely suppressed during embryogenesis via heavy DNA methylation and endogenous RNA interference (RNAi). Based on NCERT principles of molecular genetics and evolution, which of the following best characterizes this mechanism?
Options
- A.
It is a classic example of passive genetic drift, where the lack of positive selection pressure has led to the gradual deletion of the transcriptional unit from the genome.
- B.
It represents an active, adaptive regulatory silencing where methylation blocks transcription, and RNAi acts post-transcriptionally to suppress any leaky expression, preventing wasteful developmental noise.
- C.
It proves that vestigial organs arise when endogenous double-stranded RNA (dsRNA) binds directly to the promoter region of the DNA, preventing RNA polymerase from initiating transcription.
- D.
It demonstrates that the ancestral genes have undergone extensive nonsense mutations, rendering their mRNA transcripts highly susceptible to degradation by the RNA-induced silencing complex (RISC).
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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
Vestigial Organs Interpretation|RNA Interference (RNAi) Mechanism|Transcriptional Unit Boundaries
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often view vestigiality purely through the classical Neo-Darwinian lens of passive genetic drift (accumulation of mutations that destroy the gene).
This question forces them to recognize that vestigiality can also result from active epigenetic and post-transcriptional silencing.
Furthermore, it tests a critical NCERT-level molecular distinction: RNAi operates at the post-transcriptional level (binding mRNA) rather than the transcriptional level (binding DNA promoters/operators).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Evolution - Class 12 |
| Concept | Vestigial Organs Interpretation |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |