A telomere, which plays an important role in cell division is a DNA sequence at the end region of a chromosome and protects the chromosome from fraying damage or the fusing with nearby chromosomes .Each time a cell divides , DNA unwraps and its information copied but the telomere is not copied. When the cell division process is complete, the DNA reforms and the telomereis gets shorter each time this process occurs. The Hayflick limit is the number of times the duplication can take place before the telomere becomes too short potentially damaging the cell and reproduction thereof.
This shorting process is associated with ageing and cancers . However telomeres do not shorten in tissues where cells do not continually divide e.g. heart muscle.
Telomeres and telomerase , an enzyme which adds bases to the end of telomeres may be associated with aging and lifespan although animal studies in mice for example ( which have longer telomeres but a shorter lifespan than humans ) indicate that it is not a strict relationship .