Before You Begin
Question #46160
The Question
In a mutant strain of Balanoglossus, a single gene mutation exhibits pleiotropy by simultaneously arresting the development of the stomochord in the collar region and the pharyngeal gill slits in the branchial region. Based on the evolutionary relationship between Hemichordata and Chordata, which of the following statements correctly evaluates the phylogenetic significance of this pleiotropic disruption?
Options
- A.
It establishes that the stomochord is a mesodermally derived true notochord, confirming Hemichordata as a primitive sub-phylum of Chordata.
- B.
It highlights that while the pharyngeal gill slits represent a true homologous link to chordates, the stomochord is a non-homologous buccal diverticulum, justifying their placement in Non-Chordata.
- C.
It demonstrates that the pleiotropic gene regulates both the endodermally derived true notochord and the ectodermal gill slits, proving a direct chordate lineage.
- D.
It proves that the mutation disrupts a polygenic trait, leading to the simultaneous loss of the ventral solid nerve cord and the post-anal tail.
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
Hemichordata|Pleiotropy Logic|Pharyngeal Gill Slits
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often confuse the 'stomochord' with the 'notochord' due to older classification systems.
The pivot is recognizing that while Hemichordates share pharyngeal gill slits with Chordates (a true evolutionary link), the stomochord is merely an analogous structure.
Furthermore, distinguishing Pleiotropy (one gene, many traits) from Polygenic inheritance (many genes, one trait) acts as a secondary genetic trap.
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 |