The term epigenetics refers to heritable changes in gene expression that do not alter the physical DNA sequence. This essentially is a transformation in phenotype without altering the genotype. This transformation is due to genes being switched both on or off at different times. Epigenetic change is a regular and natural occurrence, but can be influenced by age, environment, lifestyle, and disease. Modifications can be unnoticeable, such as as the manner in which cells terminally differentiate to end up as skin cells, liver cells, brain cells, and more. Modifications can also be very noticeable, such as the formation of cancer or other life-threatening diseases. There are currently three known forces that initiate the silencing of genes: DNA methylation, histone modification, and non-coding RNA.
There are examples of epigenetics all around you in every day life, whether you know it or not. One very interesting way to view how a person can change as a result of epigenetics is by looking at a pair of identical twins. When a pair of identical twins is born, the two siblings share many of the same exact behaviors and physical attributes due to a nearly identical DNA sequence. The graph below shows some of the many traits identical twins share after birth.
As time progresses, twins usually begin to differentiate due to the affects of epigenetics. As twins begin to live independent lifestyles, their life choices and distinct living environments slowly begin to change them into different people compared to their similarity at birth.