Question

if you examine a natural population of bacteria, it is common to find some antibiotic - sensitive and some antibiotic - resistant strains, even if the population has never been exposed to any antibiotic. which explanation could account for this situation?
○ selection favored the resistant strain and maintained it in the population so that it would be prepared for future antibiotic exposure.
○ all of these
○ the resistant strain developed as a mutation and had no negative effect on fitness.
○ the resistant strain had greater fitness compared to sensitive strains when the antibiotic was absent.
○ the resistant strain was exposed to something in the environment that mimicked the sensitive strain, thus producing a mutation to enhance survival.

Explanation:

Mutations occur randomly in bacterial populations. If an antibiotic-resistance mutation does not reduce fitness (survival/reproduction ability) in the absence of antibiotics, it can persist in the population without selection pressure from antibiotics. This explains pre-existing resistance before antibiotic exposure. Other options are incorrect: selection cannot favor traits for future use (A); "all of these" is wrong as other options are invalid; greater fitness without antibiotics (D) is not necessary (neutral fitness suffices); mutations are not induced by mimics to enhance survival (E, mutations are random).

Answer:

C. The resistant strain developed as a mutation and had no negative effect on fitness.