Final answer:
In eukaryotic DNA replication, DNA ligase is the enzyme responsible for joining Okazaki fragments together. A mutation in DNA ligase would likely cause the impairment observed in the joining of these fragments.
Step-by-step explanation:
The eukaryotic Okazaki fragments are short sequences of DNA nucleotides that are synthesized on the lagging strand during DNA replication. They are joined together to create a continuous DNA strand. The enzyme responsible for this process is known as DNA ligase. In a situation where the joining of Okazaki fragments is impaired, it is likely that a mutation has occurred in the DNA ligase enzyme. This mutation would prevent DNA ligase from completing its role in sealing the nicks between fragments, leading to defective DNA replication.