The pesticide was withdrawn after generation 10. Populations were tracked for another 20 generations. The graph shows R allele frequency from generation 10 to 30.
Why does R decrease after pesticide is removed?
- A
Genetic drift always returns frequencies to 0.5.
- B
Insects can choose to lose the R allele.
- C
Mutations have eliminated the R allele entirely.
- Dcheck_circle
R likely carries a fitness cost in pesticide-free environments, so susceptible alleles increase.
Explanation
Many resistance alleles impose metabolic costs when the selective agent is absent, so previously favored alleles can decline once the pressure is gone.