Before You Begin
Question #45305
The Question
In a dihybrid plant (AaBb), genes 'A' and 'B' are located on the same chromosome in a cis (coupling) arrangement. A chemical mutagen completely inhibits the activity of the recombinase enzyme during meiosis. Which of the following statements regarding the genetic and cytological consequences for this plant is INCORRECT?
Options
- A.
The homologous chromosomes will fail to form functional recombination nodules during the pachytene stage.
- B.
A test cross of this dihybrid plant will yield a phenotypic ratio of 1:1:1:1 due to the complete suppression of crossing over.
- C.
Self-fertilization of this plant will result in an F2 phenotypic ratio of 3:1 rather than the classic Mendelian 9:3:3:1.
- D.
The plant will produce only two types of gametes, representing the parental gene combinations, in equal frequencies.
Check Your Answer
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
Pachytene|Mendelian Dihybrid Exceptions|Recombination_Frequency
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often blindly associate a dihybrid test cross with a 1:1:1:1 ratio.
The trap lies in failing to connect the cytological prerequisite (pachytene recombination) with the genetic outcome.
When recombinase fails, crossing over is absent, physically locking the genes into complete linkage.
This collapses the expected dihybrid ratios (9:3:3:1 and 1:1:1:1) into monohybrid-like ratios (3:1 and 1:1).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Cell Cycle and Cell Division - Class 11 |
| Concept | Pachytene Crossing Over |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |