Final answer:
The enzyme initiating the separation of DNA strands during replication is DNA helicase. When Okazaki fragments don't join correctly, DNA ligase is likely mutated. Telomerase maintains the ends of linear chromosomes.
Step-by-step explanation:
The enzyme which initiates the splitting of the double DNA strand during replication is called DNA helicase. This enzyme breaks the hydrogen bonds holding the two DNA strands together and forms a replication fork, allowing each strand to be a template for the new complementary strands. Concerning the cell strain where the joining of Okazaki fragments is impaired, the most likely mutated enzyme at the replication fork responsible for this defect is DNA ligase. This enzyme is vital for joining the Okazaki fragments on the lagging strand. As for the enzyme involved in maintaining the ends of linear chromosomes, the correct answer is telomerase, which adds repetitive sequences to the telomeres, protecting the chromosome from degradation.