ABSTRACT
The original definition of epigenetics by Waddington is already aimed at describing how factors within the developmental processes of organisms affect gene expression. Every epigenetic process described to date has two basic components: the intrinsic machinery of the cells, and the contribution of external factors. Epigenetic machineries are involved in any aspect of the body's function. Intrinsic (endogenous) and extrinsic (environmentally available) factors alter the functioning of epigenetic machineries in the developing and adult organism and, subsequently, their reproductive capacity. Many endogenous factors shown to alter epigenetic mechanisms relate to the endocrine system, having distinct roles at different ontogenetic stages. Environmental factors that are able to influence the establishment of epigenetic mechanisms, through a variety of biological pathways, include compounds such as endocrine disruptors, nutritional factors, pharmaceuticals and inorganic chemicals. In the present chapter we summarize known intrinsic and extrinsic factors that affect epigenetic regulation of gene expression, placing especial emphasis in the reproductive consequences of their actions.
