Before You Begin
Question #45596
The Question
In the classic NCERT example of industrial melanism (Biston betularia), the melanic (dark) phenotype is completely dominant over the non-melanic (light) phenotype. Suppose a hypothetical moth species undergoes a similar environmental shift (soot-covered trees), but its body color is governed by incomplete dominance, resulting in light, intermediate (grey), and dark phenotypes. If directional selection strongly favors the dark phenotype, how would the evolutionary dynamics differ from the classic Biston betularia model?
Options
- A.
The light-colored allele will be eliminated from the population much faster because it cannot be shielded from natural selection in the heterozygous state.
- B.
The population will undergo stabilizing selection instead of directional selection, as the grey heterozygotes will have the highest survival rate.
- C.
The dark phenotype will take much longer to become established because the dark allele acts as a recessive trait and must be homozygous to be expressed.
- D.
The genotypic ratio will remain strictly 1:2:1 in the surviving population due to the blending inheritance of the alleles.
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
Natural Selection Directionality|Phenotypic Variance|Biston betularia
Why This Question Is Tricky
Common Mistakes
The 'Conceptual Pivot' is the concept of the 'heterozygote reservoir'.
Students often memorize industrial melanism as directional selection but fail to realize that complete dominance protects the recessive allele from being purged.
By changing the genetic basis to incomplete dominance, the heterozygote becomes phenotypically distinct and visible to selection, fundamentally altering the rate of allele elimination.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Principles of Inheritance and Variation - Class 12 |
| Concept | Incomplete Dominance Pheno-Geno |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |