Epigenetics is the study of how changes and environmental factors experienced by an organism can affect the way genes are expressed without altering the genetic code. Epigenetics has also been linked to ageing. The reason why epigenetics affects ageing is because the DNA methylation acts as a clamp on the chromosomes, so when it comes time for the cell to replicate and unwind its chromatin from around the histones to copy the DNA, the methylation groups don’t allow that segment of DNA from being unwound. Therefore those nucleotide pairs aren’t read and the gene isn’t expressed. Interestingly DNA methylation is inherited through the germline due to a DNA methyltransferase called DNMT1, which copies methylation onto the daughter strand of DNA
