Telomere

A telomere can be defined as "The tip of a chromosome, containing a DNA sequence required for stability of the chromosome end". Telomeres are unique structures which may be present at the ends of linear chromosomes. Organisms which possess linear chromosomes encounter difficulty when it comes to complete replication of DNA ends. DNA polymerase enzyme requires an RNA primer inorder to enable itself to copy DNA (DNA copied in a 5'-3' direction). The end of DNA replication is followed by the removal of the RNA primer from the lagging strand. This RNA primer removal leads to shortening of the chromosome with each round of replication. Another cause of telomere shortening is oxidative stress. 

It is also suggested that the length of telomeres are linked to aging processes. Length of telomeres can also be affected by lifestyle and diet . Asides aging telomeres have been said to play a role in oncogenesis, the increase in telomere length as a result of inability of telomerase to be inactivated leads to cancer .