ABSTRACT
Humans with the same DNA sequence, such as monozygotic twins, and cloned animals frequently present different phenotypes and degrees of sickness penetrance. The increasingly popular term epigenetics embodies a partial explanation of both phenomena. First introduced by C. H. Waddington in 1939 to name “the causal interactions between genes and their products, which bring the phenotype into being,” it was subsequently defined as those heritable changes in gene expression that are not due to any alteration in DNA sequence. The best-known epigenetic marker is DNA methylation. The hype of epigenetic research also relates to the introduction of powerful and user-friendly techniques for the study of DNA methylation, such as sodium bisulfite modification associated with polymerase chain reaction procedures. The advent of comprehensive epigenomic technologies has given rise to the first preliminary descriptions of the epigenomes of human cells.
