Passage II
Some mutations in Escherichia coli allow the bacteria to survive exposure to an antibiotic. These antibioticresistant bacteria may have a different relative fitness (a measure of survival and reproductive success) than E. coli without mutations. Scientists conducted a study to determine the relative fitness of 5 E. coli strains—1 nonmutated (Strain U) and 4 mutated (Strains W, X, Y, and Z)—when the strains were exposed for 24 hr to each of 5 different concentrations of the antibiotic streptomycin (see Table 1). The effect of the mutation in each of Strains W−Z is listed in Table 2.
Table 1 adapted from Viktória Lázár et al., “Bacterial Evolution of Antibiotic Hypersensitivity.” ©2013 by EMBO and Macmillan Publishers Limited.
8. Based on Table 1, if Strain X had been exposed for 24 hr to a streptomycin concentration of 3 μg/mL, its relative fitness would most likely have been:
Your Answer is
Correct Answer is G
Explanation
According to Table 1, the 3 units of streptomycin concentration should be between 2 and 4 units, so the value of X should be in the range corresponding to horizontal 2 and 4, that is, 0.5~0.8