Final Answer:
The exposure of bed bug populations to DDT affected variation by causing mutations that led to the DDT resistance allele, selection through differential survival and mating preferences, and inheritance as the resistant alleles were passed down to subsequent generations.
Step-by-step explanation:
The prior exposure of bed bug populations to DDT has affected the steps of variation, selection, and inheritance within the principle of evolution by natural selection. Due to DDT exposure, mutations occurred (b), resulting in the allele conferring DDT resistance appearing in the population. These mutations represent variation. Selection was evident when DDT killed off a large proportion of the population, leaving only those with the resistant allele to survive and reproduce (a). Also, the female mosquitoes' choice of DDT-resistant male mates indicates selection for traits that enhance offspring fitness (c). Over time, the inheritance of the DDT-resistant allele ensured that future generations were also resistant (d). Lastly, the observation of purple-legged insect subgroup potentially resisting the Bt toxin supports the connection between genotypic variation and phenotypic expression in resistance (46).