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Question #45339
The Question
In diplosporous apomixis (observed in some species of Asteraceae), the megaspore mother cell (MMC) bypasses meiotic reduction and develops into an embryo sac. If you compare the ploidy and DNA content of the resulting unfertilized apomictic egg cell (assuming it is in the G1 phase) with a human primary oocyte arrested at the dictyotene stage of Prophase I, which of the following statements is correct?
Options
- A.
Both cells are diploid (2n); however, the apomictic egg cell has a DNA content of 2C, whereas the arrested primary oocyte has a DNA content of 4C.
- B.
Both cells are diploid (2n) with a DNA content of 4C, as both represent a state of permanent meiotic arrest prior to the first reductional division.
- C.
The apomictic egg cell is haploid (n) with 2C DNA due to aborted meiosis, whereas the arrested primary oocyte is diploid (2n) with 4C DNA.
- D.
The apomictic egg cell is diploid (2n) with 4C DNA, whereas the arrested primary oocyte is haploid (n) with 2C DNA because homologous chromosomes have already paired.
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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
Diplospory|Meiotic_Arrest|Primary_Oocyte_Comparison
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: The question tests the synthesis of three distinct NCERT concepts: Apomixis (Class 12, Ch 2), Oogenesis arrest points (Class 12, Ch 3), and Cell Cycle DNA content tracking (Class 11, Ch 10).
The common misconception is conflating ploidy (chromosome number, 2n) with DNA content (chromatid number, 2C vs 4C).
Students often fail to recognize that a cell arrested in Prophase I has already undergone S-phase duplication (hence 4C), whereas a newly formed mitotic cell in G1 (like the apomictic egg) is 2C.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Sexual Reproduction in Flowering Plants - Class 12 |
| Concept | Apomixis Genetics |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |