Telomerase Rna

[mage lang=”en|es|fr|en” source=”flickr”]telomerase rna[/mage]
Why do telomeres eventually shorten as chromosome replication occurs?

I know that telomerase adds repetative sequences using a reverse RNA transcriptase to cover the gap on the 3 prime end, but why does this gap eventually form?

in order to change RNA to DNA, there must be another DNA strand in front of the RNA primer. This happens at all the sites of the lagging strand, but it doesn’t happen at the end where the last RNA primer is attached. Ultimately, that RNA is destroyed by enzymes that degrade RNA left on the DNA. Thus, a section of telomeres is lost during each cycle of replication at the 5′ end of lagging strand.

Looks like all gaps can be covered except at the very end.