Fig. 1

Three main epigenetic mechanisms: A DNA methylation, in which DNA methyl transferase enzymes (DNMTs) transfer a methyl group to carbon 5 of cytosine residues B Histone modifications such as acetylation, methylation and phosphorylation are accomplished by their specific transferase enzymes on certain peptide residues C most known non-coding RNA action maybe the X chromosome inactivation which occurs in female mammals due to dosage compensation. In this process, one of the X chromosomes is randomly transcribed on the XIST gene locus; the XIST long non-coding RNA–protein complexes bind to the X chromosome in special places called ‘entry sites’, which plays a major role in the formation of inactivated X chromosome or ‘Barr body’ (the red circle). Designed by BioRender.com