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Question #46778
The Question
A quantitative trait in a plant species is normally controlled by three polygenes (A, B, and C) located on different chromosomes, yielding a classic continuous, bell-shaped phenotypic distribution in the F2 generation. A radiation-induced pericentric inversion occurs, bringing loci A and B onto the same chromosome in extremely tight physical proximity near the centromere. If individuals heterozygous for this new arrangement are crossed, how will the F2 phenotypic distribution most likely deviate from the expected polygenic pattern?
Options
- A.
The bell-shaped curve will remain unchanged because the additive effect of the dominant alleles is independent of their physical chromosomal location.
- B.
The distribution curve will skew and exhibit fewer phenotypic classes because the independent assortment of loci A and B is severely restricted.
- C.
The trait will shift to a qualitative inheritance pattern, exhibiting a classic 9:3:3:1 ratio due to the newly established dominant-recessive epistasis.
- D.
The population will exhibit a bimodal distribution because the inversion inherently causes the deletion of the unlinked C locus.
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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
Centromere Positionality|Polygenic Inheritance Curve|Meiotic Reductional Division
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize from NCERT that 'polygenic traits show a bell-shaped curve' and 'alleles have an additive effect'.
The trap is failing to synthesize that the continuous shape of this curve fundamentally depends on the independent assortment of these loci.
The common misconception is assuming that as long as the genes are present, their additive nature alone guarantees continuous variation, ignoring the cytogenetic reality that linkage (linkage disequilibrium) restricts the random combination of these additive alleles.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Cell – The Unit of Life - Class 11 |
| Concept | Centromere Positionality |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |