The phenotype of an organism is determined not only by its genotype but is also influenced by the epigenetic status of the inherited DNA, also called epigenotype. It depends on the chromatin structure and its modifications such as methylation and acetylation.

Listen to Professor Professor Randy Jirtle's explanation of Epigenetics.



Levels of biological regulation
Till the recent cognition that the eukaryotic genome is more flexible and complex than assumed, for a long time the "one-gene-one-protein concept" has been the central dogma of molecular biology.
Often one gene codes for more than one protein and every single gene probably needs feedback and regulation by many others for proper function.
Some proteins activate genes by adding acetyl- or methyl groups to DNA, others, so called transcription factors, interact with genes by direct binding to DNA. A key function of chromatin proteins is the packing of DNA and via slight structural histone modifications, gene expression is switched on or off due to facilitated accessibility by the transcription machinery.
Apart from these special proteins, small RNA molecules (eg. micro RNA, nucleic RNA) become object of scientific interest since these RNAs are able to regulate and modify gene expression and thus, play a crucial role in cell differentiation processes.


In general, three different mechanisms of gene activity or biological regulation, responsible for the determination of complex phenotypes, can be distinguished:

• Monogenetic mechanism: This is the one-gene-one-phenotype way. This mechanism is often influenced by environment or other genes (e.g. sickle-cell anaemia, Duchenne's muscle dystrophy)

• Polygenetic mechanism: The phenotype is determined by many interacting genes.

• Epigenetic mechanism: This mechanism appears much more complex than mere gene-gene interaction. Epigenetics includes also interaction between genes and proteins, both, of course, permanently influenced by the environment. Epigenetic regulation is preliminarily driven by changes of the methylation pattern, function of DNA-binding proteins, or chromatin structure.

After the achievements of the Human Genome Project, an international Human Epigenome Project has been initiated to establish a genome-wide reference map of time and tissue specific DNA-methylation pattern, and, besides, the Epigenome Network of Excellence, founded by the EU.

For further information visit Epigenetic research.