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?
the resistant strain was exposed to something in the environment that mimicked the sensitive strain, thus producing a mutation to enhance survival.
the resistant strain had greater fitness compared to sensitive strains when the antibiotic was absent.
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.

Explanation:

• Option 1: Mutations are random and not directed by mimicking something in the environment.
• Option 2: If the resistant strain had greater fitness in the absence of antibiotics, it would have outcompeted the sensitive strains, but this is not the case as both exist.
• Option 3: Natural selection does not act in anticipation of future events like antibiotic exposure.
• Option 5: Mutations occur randomly. If a mutation for antibiotic resistance occurs and it has no negative effect on the bacteria's fitness (i.e., it doesn't make the bacteria less able to survive and reproduce in its normal environment), then it can persist in the population.

Answer:

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