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Question #45849
The Question
In a large, panmictic population of a diploid organism, two unlinked genes exhibit a classic 9:3:3:1 phenotypic ratio. Following a severe environmental catastrophe, only a few individuals survive to rebuild the population. In subsequent generations, the population drastically deviates from the 9:3:3:1 ratio, despite the genes remaining on separate chromosomes. Which of the following best explains this deviation?
Options
- A.
The bottleneck effect induced physical linkage between the genes, preventing independent assortment during Anaphase I.
- B.
Stochastic sampling error drastically altered allele frequencies, violating the large population size assumption required for Mendelian probabilistic outcomes.
- C.
Non-random mating among the survivors significantly increased the proportion of heterozygotes, skewing the genotypic distribution.
- D.
The catastrophe acted as a directional selection pressure, which inherently eliminates recessive alleles in small populations.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Evolutionary_Exception
Tackle problems where standard rules evolve or change based on specific environmental constraints.
Concepts Behind This Question
Mendelian Dihybrid Exceptions|Allele Frequency Drift
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize that 'unlinked genes always yield a 9:3:3:1 ratio' without realizing that Mendelian ratios are statistical models.
The trap relies on failing to distinguish between the cellular mechanism of independent assortment (which remains intact) and the population-level statistical outcome (which is destroyed by the stochastic sampling error of genetic drift in small populations).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Principles of Inheritance and Variation - Class 12 |
| Concept | Mendelian Dihybrid Exceptions |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |