Evolutionary sequence for antibiotic resistance

Steps:

• Mutations in bacterial DNA create new resistance alleles, increasing genetic variation within the DNA (4).
• These mutations spread through reproduction, increasing overall genetic variation in the population (3).
• Introduction of the new antibiotic applies selection pressure, killing non-resistant bacteria (1).
• Surviving resistant bacteria reproduce, increasing the frequency of the resistance allele in the population (2).

Why D is correct:

• It matches the Darwinian process: mutation generates variation (4→3), selection via antibiotic acts (1), then allele frequency rises (2).

Why the others are wrong:

• A: Begins with allele frequency increase (2), impossible without prior variation and selection.
• B: Starts with antibiotic introduction (1), but resistance alleles must pre-exist via mutation.
• C: Places population variation (3) before DNA variation (4), reversing the mutation source.

Final answer: D