A population of crop-damaging insects was repeatedly sprayed with a synthetic chemical insecticide over several years. Initially, the chemical killed almost all insects, but after consecutive generations, the population became predominantly resistant to the chemical. According to modern evolutionary theory, which of the following best explains how this resistance developed within the gene pool?
- Pre-existing random gene mutations provided resistance in a few individuals, and natural selection increased the frequency of these resistant alleles over generations.Answer
- BInsects exposed to the pesticide developed somatic tolerance during their lifetimes and passed these acquired adaptations to their offspring.
- CThe chemical insecticide acted directly on non-resistant insects to induce specific target mutations that counteracted the toxin.
- DSexual reproduction and genetic recombination deliberately synthesized novel gene alleles to neutralize the chemical structure of the pesticide.
Answer
Pre-existing random gene mutations provided resistance in a few individuals, and natural selection increased the frequency of these resistant alleles over generations.
According to modern evolutionary theory, random gene mutations introduce variation into a gene pool independently of environmental needs. When an environmental stressor such as an insecticide is introduced, it acts as a selective pressure. Individuals already possessing the resistant allele survive and reproduce, passing the genetic trait to their offspring. Over generations, the frequency of the resistant allele increases within the population.
Step-by-Step Solution
Key Concept
Modern Evolutionary Theory (Neo-Darwinism) and Natural Selection on Genetic Variation