Chapter 52 – Epigenetics in Reproduction and Development∗

Epigenetics can be defined as the study of mitotically or meiotically heritable changes in gene function that cannot be explained by changes in the DNA sequence. Epigenetic inheritance involves the transmission of information (epigenetic mark) not encoded in the DNA sequence, from parent cell to daughter cells and from generation to generation. Epigenetic modification of the genome is a dynamic process, and it is not restricted to any specific part of an organisms' life cycle; rather, it begins at the level of the developing germ cells in the embryo and continues throughout life. Specific epigenetic marks can be laid down in the genome by a variety of environmental factors ranging from maternal nutrition during pregnancy to postnatal care and by exposure to environmental chemicals. It is the transgenerational persistence of epigenetic marks that make the study of epigenetics important to many branches of science including biology, toxicology, psychology, and social sciences. Although much needs to be understood in terms of correlative effects vs. causal effects between exposure to various environmental factors and epigenetic modifications, advances in epigenetics have nonetheless provided a molecular basis for explaining the “nurture” element of the “Nature (genetics) versus Nurture (environment)” debate and helped transform this debate from a philosophical one to a scientific one.