As eukaryotic cells divide, the protective ends of the linear chromosomes, the telomeres, gradually shorten with each cell division. When a critical telomere length is reached, the cells are signalled into senescence, an irreversible state of quiescence. Thus, telomere length has emerged as a replica-tive clock within each population of cells and the tissues and organs they form in vitro. Consequently telomere length has become accepted as a biomarker for biological ageing in vivo. Although chronological ageing per se does not parallel biological ageing, there are no accurate and reliable biomarkers to distinguish between both types of ageing. The question remains whether telomere dynamics is a determinant or merely a predictor of human biological age over and above chronological ageing.
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