Our body consists of various tissues such as skin, stomach, and liver, and these tissues consist of different types of cells. Although essentially all the cells have the same genetic information, cells acquire different characteristics that persist for a life time. This is because different types of cells have added different sets of stable marks to genes that should be used (expressed) and also to genes that should not be used. Epigenetics is the discipline that elucidates the characteristics of these marks. As symbolized by the fact that gastric cells cannot be transdifferentiated into skin cells, stable transmission in somatic cells is one of the major characteristics of epigenetic marks.
In a cell, DNA is present circling approximately twice around proteins called histones. Epigenetic marks consist of the mark on DNA (DNA methylation ) and marks of histones (histone modifications) (Fig. ).
Fig. DNA methylation and histone modifications
As epigenetic marks, DNA methylation and histone modifications are known. DNA is methylated at cytosines at CpG sites.