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Question #45590
The Question
A plant breeder performs a back cross between an F1 hybrid (Aa) and its homozygous dominant parent (AA) to fix a commercially valuable dominant phenotype. While the expected genotypic ratio is 1 AA : 1 Aa, the observed ratio in the surviving mature progeny is drastically skewed to 0.1 AA : 1 Aa. Assuming no environmental anomalies, which of the following genetic principles best explains this deviation?
Options
- A.
The gene exhibits pleiotropy, where the homozygous dominant state negatively impacts a secondary vital metabolic pathway, reducing viability.
- B.
The dominant allele A is tightly linked in cis-configuration to a recessive lethal allele on the same chromosome.
- C.
The trait is governed by polygenic inheritance, causing the AA genotype to be phenotypically masked by hypostatic genes.
- D.
The F1 hybrid experienced a failure of segregation during Anaphase I, leading to a disproportionate loss of A-bearing gametes.
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
Pleiotropy Logic|Test Cross vs Back Cross Ratios
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize that 'lethal alleles skew ratios' (Option B trap) without realizing that a homozygous dominant parent (AA) cannot carry a cis-linked recessive lethal allele without being dead itself.
The question tests the synthesis of back-cross mechanics with the concept of pleiotropic fitness costs, where a single gene's multiple effects (one beneficial, one detrimental) alter expected Mendelian survival ratios.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Principles of Inheritance and Variation - Class 12 |
| Concept | Test Cross vs Back Cross Ratios |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |