Genetics is the branch of biology that deals with the transmission and variation of inherited characteristics. Genetic changes were supposed to be exclusively linked to specific chromosomal or DNA changes that were transmitted through generations. The discovery and characterization of the interactions between the genome and the environment is changing our understanding of genetics and the way we think about transmission and heredity. Indeed, epigenetics, this new field of genetics, describes heritable changes in gene expression that occur without a change in the DNA nucleotidic sequence. It is now considered to play an essential role in the expression of specific phenotypes and in their potential transmission. We can now understand phenotypes as based on genotypes and epigenotypes.