A new and effective antibiotic becomes widely used for a particular species of bacteria. After some time, an antibiotic-resistant strain of the bacteria becomes prevalent. Which mechanism explains this phenomenon?
The bacteria undergoes genetic drift, leading to formation of a new gene pool and thus evolving a new characteristic.
Although less common previously, the resistant strain becomes more prevalent due to natural selection.
The bacteria undergoes genetic flow, thus creating a new gene pool and evolving into a new species.