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Question #45285
The Question
In a mutant strain of a diploid organism, a genetic defect completely inhibits the formation of recombination nodules during the pachytene stage of meiosis. If a dihybrid organism (AaBb) with genes A and B located on the same chromosome in a cis arrangement is test-crossed, which of the following represents the correct phenotypic ratio of the progeny and the effective genetic map distance between genes A and B?
Options
- A.
1:1:1:1 ; Map distance is 50 cM
- B.
1:1 (Parental types only) ; Map distance is 0 cM
- C.
9:3:3:1 ; Map distance is proportional to physical distance
- D.
1:1 (Parental types only) ; Map distance is equal to their physical distance in base pairs
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
Recombination Nodule Function|Linkage Group Calculation|Chromosomal Theory of Inheritance
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Distinguishing between physical distance and genetic map distance.
Students often assume physically distant genes must have a map distance > 0.
However, Sturtevant's genetic mapping relies entirely on crossover frequency.
A failure in recombination nodule formation drops the recombination frequency to zero, making the genetic map distance 0 cM and resulting in complete linkage, regardless of the physical base-pair separation.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Cell Cycle and Cell Division - Class 11 |
| Concept | Recombination Nodule Function |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |