Consider a bacterial population where a resistance gene is initially present in 0.1% of cells but on a conjugative plasmid with high transfer rate. After several days in an antibiotic-rich environment, which pattern of spread would you expect compared with a scenario where the same resistance gene is a chromosomal mutation present in 0.1%? Choose the best analysis.

• A. Both plasmid and chromosomal resistance will spread identically because selection imposed by antibiotics affects all genetic contexts equally and horizontal transfer rarely changes frequencies within short time frames in dense populations.
• B. Neither will spread because antibiotics select only for phenotypic tolerance that is not genetically heritable, therefore genetic location is irrelevant for short-term population dynamics under treatment.
• C. A chromosomal mutation will always spread faster because mutations are more stable and cannot be lost by segregation, whereas plasmids are too unstable under selection to be maintained in any host over multiple generations.
• D. The plasmid-borne resistance will spread to many unrelated strains rapidly via conjugation and selection, producing faster and broader dissemination than the chromosomal mutation which spreads only by vertical transmission and therefore more slowly and clonally.

Answer: (D)