Frequency of an antibiotic-resistance allele in a bacterial population is monitored before and after antibiotic introduction.
What best explains the rapid rise in resistance allele frequency after antibiotic introduction?
- A
Genetic drift unrelated to the antibiotic
- Bcheck_circle
Strong directional selection favoring pre-existing resistant variants
- C
Hardy-Weinberg equilibrium being maintained
- D
Bacteria mutated specifically in response to the antibiotic to acquire resistance
Explanation
Pre-existing resistance alleles, present at low frequency, were strongly favored by selection once antibiotics were introduced. Mutations are random with respect to need; selection acts on standing variation.