[Pre-programmed genes]

Cells feel good and carry on perfect functions when they contain the right types of proteins in the right concentration, at the right time and sites. There are mechanisms that ensure the right level of gene expression in the different cell types: the formation of protein molecules based on the DNA-encoded genetic information. Gene expression can also be regulated through the compactness of chromatin, i.e. the accessibility of the genes. The chromosomes are repositories of the genetic information - the sequence of base pairs - and also of the so-called epigenetic mechanisms that control gene expression through the regulation of chromatin compactness. The epigenetic mechanisms operate through DNA methylation and/or the regulation of chromatin compactness. The present overview takes a look into the phenomenon of epigenesis. It summarizes how genetic crosses reveal the involvement of epigenesis, explains its meaning and impact on life of the organisms. An understanding of epigenesis provides guidance to improve our life. Orv Hetil. 2017; 158(34): 1323-1330.