Q67 DDT is an insecticide that was used extensively in the m

Q6.7. DDT is an insecticide that was used extensively in the mid-1900s to kill mosquitoes. It was very effective at first, but after a few decades DDT became less effective at killing mosquitoes because many populations had evolved resistance to DDT. Which of the following conditions would biologists say was required for the evolution of DDT resistance in a population?

(a) A few mosquitoes in the population were resistant to DDT before it was ever used.

(b) Mosquitoes in the population learned to adapt to the high levels of DDT in the environment.

(c)The mosquito population needed to evolve DDT resistance in order to avoid extinction.

(d) Exposure to DDT caused specific, nonrandom mutations for DDT resistance within the population.

A and C both seem like good answer but which one is better?

Solution

Answer:- Option A

A few mosquitoes in the population were resistant to DDT before it was ever used.

Exp:- A few mosquitoes were already carrying mutation that is they were mutants which give them resistance against DDT. So wheb DDT was applied all susceptible mosquitoes died excpt those which wer mutants there by only these survive now these mutants reproduce and utilize resource which are abundant and ultimately produce large number of resistant population. This wad best described by lederberg\'s replica plating experiment (DDT only acts as selecting agent that selects mutants already present in the pop. It doesn\'t cause mutation.