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Question #47390
The Question
The human vertebral column consists of 26 serially arranged units. The specific identity and number of these vertebrae along the craniocaudal axis (C7, T12, L5, S1, C1) are established during embryogenesis, while their structural integrity is maintained post-puberty. Consider two clinical cases: Case X: An individual is born with a transformation of the first lumbar vertebra into a thoracic-like vertebra bearing ribs. Case Y: A 30-year-old male with Klinefelter syndrome (47, XXY) presents with severe vertebral compression fractures but a normal vertebral formula. Which of the following statements accurately explains the biological basis of these observations?
Options
- A.
Case X is caused by a mutation in Hox genes altering developmental specification, whereas Case Y involves impaired homeostatic maintenance of bone density due to an altered testosterone-to-estrogen ratio.
- B.
Case X results from a failure of endochondral ossification during puberty, whereas Case Y is due to a homeotic gene mutation affecting the craniocaudal axis.
- C.
Both cases represent a disruption in the embryonic axial symmetry regulated by the sequential expression of homeobox genes.
- D.
Case X is due to an abnormal hormonal milieu during fetal development, whereas Case Y is caused by the misexpression of Hox genes during adulthood.
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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
Vertebral Column Formula|Down/Klinefelter/Turner Syndrome Karyotypes
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Distinguishing between 'developmental specification' (embryonic patterning via Hox genes) and 'homeostatic maintenance' (post-natal structural integrity via hormones).
A common misconception is that chromosomal anomalies like Klinefelter syndrome might alter fundamental body plans (like vertebral formulas), or failing to recognize that bone density maintenance is a continuous, hormone-dependent process distinct from embryonic bone formation.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Locomotion and Movement - Class 11 |
| Concept | Vertebral Column Formula |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |