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Question #46161
The Question
Hemichordates possess a rudimentary structure in the collar region called the stomochord. Evolutionary models suggest that during the divergence of early deuterostomes, a small, geographically isolated founder population rapidly evolved a true notochord, leading to the emergence of Chordates. Which of the following accurately contrasts these two structures and identifies the evolutionary mechanism most likely responsible for the rapid fixation of this novel trait?
Options
- A.
The stomochord is a mesodermal outgrowth, whereas the notochord is endodermal; the rapid fixation of the notochord occurred via the Sewall Wright effect.
- B.
The stomochord is a buccal diverticulum, whereas the notochord is mesodermally derived; the rapid fixation of the true notochord was primarily driven by allele frequency drift.
- C.
Both structures are mesodermally derived, but the notochord is solid and dorsal; the rapid divergence was driven by high gene flow and stabilizing selection.
- D.
The stomochord is a buccal diverticulum, whereas the notochord is ectodermally derived; the rapid fixation of the trait was due to a genetic bottleneck increasing heterozygosity.
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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
Hemichordata|Allele Frequency Drift|Evolutionary Notochord Progression
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Integrating Animal Kingdom anatomy with Evolutionary Genetics.
Students frequently confuse the embryonic origins of the stomochord and notochord (mesodermal vs. non-mesodermal).
Furthermore, the trap tests the application of Hardy-Weinberg principles: recognizing that 'small, isolated populations' are the primary domain of Genetic Drift (Allele Frequency Drift), whereas large populations are governed by selection.
Option D contains a secondary trap by stating bottlenecks 'increase' heterozygosity, when in fact they deplete genetic variation.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Animal Kingdom - Class 11 |
| Concept | Hemichordata Evolutionary Link |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |