[Epigenetics, principles and examples of applications].

Since the discovery of DNA as the support of genetic information, the challenge for generations of life scientists was to understand the mechanisms underlying the process that translate the sequence of a gene to a phenotype. In the 1950s, the concept of epigenetics was defined by the British biologist Conrad H. Waddington as the study of "epigenesis" that governs the biological processes involved in the development of any organism. The term epigenetics, now best defined as "above the DNA sequence" reflects the gene-environment interactions by which genes determine traits. Since, its first description, studies underlying the mechanisms involved in these processes has led to an increasing understanding of the regulation all genome transactions such as transcription, replication, repair and the biological pathways coordinated by these mechanisms. We will discuss here the main principles regulating epigenetic processes, their roles in physiology, their evolution over the life time and their implications in medicine.