Final answer:
DNA does not shorten after replication because the enzyme telomerase extends the lagging strand at the ends of chromosomes, allowing for complete replication without gene loss. Over time, however, telomeres can still shorten, contributing to aging.
Step-by-step explanation:
The question concerning why DNA does not shorten after replication can be explained by discussing the action of the enzyme telomerase during telomere replication. In eukaryotic cells, as the replication fork moves at a rate of 1000 nucleotides per second, the issue arises when nearing the end of a linear chromosome. The leading strand can be continuously synthesized till the end of the chromosome, but the lagging strand needs primers to initiate the formation of Okazaki fragments. As there's no place to add a primer at the very end, the lagging strand risks getting progressively shorter with each replication cycle.