SAT Subject Biology Practice Question 457: Answer and Explanation
7. A population of ampicillin-resistant bacteria (Strain 1) is grown in a laboratory and is infected with a virus. The bacterial population begins to decline as the virus initially goes through the lytic cycle, then rebounds as the virus integrates into the bacterial chromosome to begin the lysogenic cycle.
The bacteria reproduce normally until they are heat-shocked. The rapid increase in temperature causes the virus to remove itself from the bacterial genome and enter the lytic cycle. Within several hours all bacteria are dead and a free virus is found in high concentration in the bacterial growth medium.
This free virus is used to infect a population of bacteria that is sensitive to ampicillin (Strain 2). After the expected decrease and rebound of this bacterial population (as above), the rebounded population was found to be ampicillin-resistant.
The acquisition of ampicillin resistance by bacterial Strain 2 is due to
Correct Answer: E
E Know your terms for genetic variability in bacteria! Transduction is the transfer of DNA (and therefore of new traits, such as resistance to an antibiotic) through viral infection. Choice A, evolution, is true-the bacterial population has evolved. However, the question asks for the more specific answer. The bacteria are not a new species; they have simply acquired a new trait (choice B is eliminated). Conjugation (choice C) is the transfer of DNA between two different strains of bacteria and requires that the two different strains be mixed together at some point. This did not occur in the experiment. Transformation (choice D) is a situation in which bacteria take up naked DNA from the environment; again, this did not occur here.