Question

The restriction enzymes of 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, this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA in attacking bacteriophages.

34) Over the course of evolutionary time, what should occur?
A) Methylated DNA should become fixed in the gene pools of bacterial species.
B) Methylated and nonmethylated strains should be maintained among both bacteria and bacteriophages, with ratios that vary over time.
C) Nonmethylated DNA should become fixed in the gene pools of bacteriophages.
D) Methylated DNA should become fixed in the gene pools of bacteriophages.
E) Both A and B are correct.

Answer 1

In the evolutionary arms race between bacteria and bacteriophages, both methylated and nonmethylated strains will continue to exist, with a dynamic balance that varies over time due to constant coevolution.

B is correct

Step-by-step explanation:

Over the course of evolutionary time, the interactions between bacteria and bacteriophages will likely result in a dynamic relationship where both methylated and nonmethylated strains of these organisms will continue to exist with varying ratios over time. The coevolutionary arms race implies that when one bacterial strain develops a defense mechanism, such as producing restriction enzymes that degrade non-methylated DNA, phages will evolve to counteract this by methylating their own DNA.

As soon as these new phage strains become more prevalent, selection pressure will favor bacteria with the ability to degrade methylated DNA. This cyclical process means that neither methylated DNA nor nonmethylated DNA will become entirely fixed within the gene pools of bacterial species or phages. Therefore, the most applicable answer is B) Methylated and nonmethylated strains should be maintained among both bacteria and bacteriophages, with ratios that vary over time.

Answer 2

D) Methylated DNA should become fixed in the gene pools of bacteriophages.