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Question #45587
The Question
In a genetic study, an generation from a dihybrid cross exhibits a strict 3:1 phenotypic ratio for two distinct traits, completely lacking recombinant phenotypes. Initially, this is hypothesized to be the result of complete physical linkage between two separate genes. However, RFLP (Restriction Fragment Length Polymorphism) analysis reveals that a single point mutation has simultaneously abolished an EcoRI recognition site and altered both traits. Which of the following best explains this deviation from the expected 9:3:3:1 Mendelian ratio?
Options
- A.
The EcoRI site mutation prevents the formation of the synaptonemal complex, thereby halting crossing over between two linked genes.
- B.
The traits are not controlled by two separate genes; rather, the deviation is due to pleiotropy where a single locus influences multiple traits.
- C.
The mutation induced a reciprocal translocation, physically linking two previously independently assorting chromosomes.
- D.
The absence of the EcoRI site prevents the independent assortment of chromosomes during Anaphase I, leading to a pseudo-linkage.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Comparative_Analysis
Sharpen your ability to evaluate multiple scenarios and distinguish between competing potential answers.
Concepts Behind This Question
Mendelian Gamete Frequency|Restriction Endonuclease Nomenclature|Ori Sequence Stringency
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often reflexively associate a 3:1 dihybrid F2 ratio with complete linkage, ignoring pleiotropy.
The question uses a restriction endonuclease site mutation (RFLP) as molecular proof that only a single locus is involved, bridging classical Mendelian genetics (Principles of Inheritance) with molecular markers (Molecular Basis of Inheritance).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Principles of Inheritance and Variation - Class 12 |
| Concept | Mendelian Gamete Frequency |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |