Year 10 Science · Unit 1 · Lesson 12
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Learning Goals
Read the graph
Data: Based on Kettlewell (1955–1956), Heredity, industrial melanism in Biston betularia.
(a) Describe the change in dark moth frequency between the two time periods. What was the selection pressure responsible for this change?
(b) Predict what would happen to the moth population if air pollution laws cleaned the trees and lichen returned. Explain your reasoning using natural selection.
Scenario
A patient in a Brisbane hospital is prescribed a 10-day course of antibiotics for a chest infection. After 5 days the patient feels much better and stops taking the antibiotics. There were originally 10 million bacteria in their lungs, approximately 99% were susceptible to the antibiotic, but about 1% (100,000) carried a random mutation that gave them partial resistance. The partial-resistance mutation is heritable.
(a) Using Darwin's postulates, trace what happens to the bacterial population over the following 6 months. Why does the resistant strain eventually dominate?
(b) Explain in one sentence why the antibiotic did not create the resistance mutation, even though it seems that way.
Wrap Up
In one sentence, explain why finishing a full course of antibiotics helps slow the evolution of antibiotic resistance.