Final answer:
Telomerase is the enzyme that attaches repeat sequences to the ends of chromosomes, preventing them from shortening during cell division.
Step-by-step explanation:
The enzyme that prevents chromosomal shortening by attaching a repeat sequence to the ends of chromosomes is telomerase. This enzyme plays a crucial role in maintaining the integrity of linear chromosomes by adding repetitive sequences to the telomeres, which are the ends of chromosomes. Telomerase has a built-in RNA template that it uses to extend the 3' end of the DNA strand, allowing DNA polymerase to complete the replication of chromosome ends. Without this process, chromosomes would become progressively shorter with each cell division, potentially leading to the loss of important genetic information.