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Question #45593
The Question
In a genetic mapping experiment using a test cross, two linked genes, P and Q, are known to be separated by a substantial physical distance on a chromosome. However, the observed recombination frequency is unusually low. Cytological analysis reveals the recent integration of a large, high-copy-number transposable element between genes P and Q. Which of the following best explains the impact of this integration on the linkage map?
Options
- A.
The calculated map distance will overestimate the true physical distance because the added DNA sequence provides more sites for the synaptonemal complex to form.
- B.
The calculated map distance will underestimate the true physical distance because the transposon induces localized heterochromatinization, suppressing chiasma formation.
- C.
The linkage map remains unaffected because recombination frequency is strictly dependent on the number of base pairs and independent of chromatin condensation.
- D.
The integration abolishes linkage completely, forcing genes P and Q to assort independently due to steric hindrance during Anaphase I.
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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
Plasmid vs Chromosomal DNA|Test Cross vs Back Cross Ratios
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often fall for the 'Quantitative Trap' by assuming that 'more physical DNA (due to insertion) automatically equals greater distance and higher recombination frequency'.
This question tests the NCERT-Plus synthesis of Linkage (Principles of Inheritance) with Chromatin Structure (Molecular Basis of Inheritance), highlighting that the epigenetic state (heterochromatin) overrides simple physical distance by suppressing recombination machinery.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Principles of Inheritance and Variation - Class 12 |
| Concept | Test Cross vs Back Cross Ratios |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |