Final answer:
A mutation is a random error in gene replication, and the enzyme likely mutated in the scientist's experiment is DNA polymerase, which can introduce several types of DNA sequence changes.
Step-by-step explanation:
A random error in gene replication is known as a mutation. The scientist in the scenario you've described has found many errors in the replicated DNA of bacterium's daughter cells. These errors are indicative of a mutation in one of the enzymes involved in DNA replication. The correct enzyme that is most likely to have acquired a mutation in this case would be DNA polymerase, as it is responsible for adding nucleotides to a growing DNA strand during replication. If a mutation occurs in the DNA polymerase, it can lead to spontaneous errors that can result in a variety of mutations, such as substitutions, deletions, insertions, and expansions, all of which change the DNA sequence.