Restriction enzymes in bacteria protect the bacteria from successful attack by bacteriophages, whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent, they in turn select for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. Which of the following factors is most likely to cause the changes?
A) frequency-dependent selection
B) evolutionary imbalance
C) heterozygote advantage
D) neutral variation

Question

Quizplus · Accepted Answer

Frequency-dependent selection is most likely to cause these changes because the success of the bacteria or bacteriophages depends on the relative frequencies of the different types (methylated vs. non-methylated) in the population. As one type becomes more prevalent, it selects for the opposite type in the other population, leading to a cyclical pattern of adaptation and counter-adaptation.

Restriction Enzymes in Bacteria Protect the Bacteria from Successful Attack