What is Mean Telomere Length?
Telomeres are repetitive nucleotide sequences (TTAGGG in vertebrates) and associated proteins that cap the ends of chromosomes, protecting coding DNA from degradation and end-to-end fusion. With each somatic cell division the telomere shortens by 50–200 base pairs because DNA polymerase cannot fully replicate the lagging strand; this replicative attrition eventually triggers senescence or apoptosis. Telomerase, the reverse transcriptase that adds telomeric repeats, is active in germ cells and stem cells but largely repressed in most somatic tissues. Telomere length is thus a marker of cumulative replicative history and is influenced by inherited length, chronological age, oxidative stress, inflammation, and lifestyle factors.