After a strain of bacterial cells is exposed to a chemical mutagen, only 30% of the cells produce new colonies that continue to grow. Which of the following can be concluded?

A. Some cells underwent advantageous mutations

B. Some cells underwent neutral mutations

C. Some cells underwent lethal mutations

D. Some cells underwent deleterious mutations

The answer is; A

Most of the bacteria cells were affected by the mutagen that disrupted their DNA through mutations. Most of the mutations were deleterious/lethal/disadvantageous leading to the death of a higher proportion of the bacterial colony. However, of the many mutations caused by the mutagen, some were advantageous - meaning they probably protected the cells from the mutagen. These were able to continue reproducing and formed a new mutant colony.