Describe the epigenetic marks that occur on histones

Two main types of epigenetics involving histones: methylation and acetylation.

Acetylation of histones is known to increase the expression of genes through transcription activation. The opposite is true for their deacetylation.

Histone methylation is defined as the transfer of one, two, or three methyl groups from S-adenosyl-L-methionine to lysine or arginine residues of histone proteins by histone methyltransferases. In the cell nucleus, when histone methylation occurs, specific genes within the DNA complexed with the histone may be activated or silenced.