Final answer:
DNA ligase is the enzyme that attaches Okazaki fragments on the lagging strand during DNA replication. If this process is impaired, a mutation in DNA ligase is the likely cause.
Step-by-step explanation:
The enzyme responsible for attaching the Okazaki fragments together on the lagging strand during DNA replication is DNA ligase. This enzyme acts after DNA polymerase I replaces the RNA primer with DNA. DNA ligase then seals the gaps between the Okazaki fragments, effectively joining them into a single DNA molecule. If there is an impairment in the joining of Okazaki fragments, it is likely due to a mutation in the DNA ligase enzyme.