entire chromatin complex, including both the DNA and its protein scaffolding, epigenetics takes all of this into consideration. Third, epigenetics is “mitotically or meiotically heritable changes in gene expression that are not coded in DNA itself.” Gene expression states can be passed on from one cell generation to the next, which happens, for example, during embryonic development, when cells differentiate and then reproduce to form lines of specialized cells (e.g., nerve cells and muscle cells), each of which is defined by specific genes. These genes can be either activated or silent. Gene expression states are heritable, making it possible to express traits that are not dependent on the expression of a given gene per se.

In short, epigenetics describes the way in which cells store and pass on information that is not coded in the DNA sequence itself but rather in various modifications made to the DNA and, more generally, to the chromatin complex containing it.

Epigenetics is thus an important tool for nutrigenomics because it offers a way of understanding how nutrients interact at the molecular level with the genome to create long-lasting effects. “Epigenetic regulation is a mechanism that allows the genome to integrate intrinsic signals and environmental signals. It is a way the genome interacts with the environment. So, what you ate for lunch has found its way to change in some very subtle way the epigenetic state of your DNA.” That, in turn, is related to how diet can affect health and, in particular, the risk of certain diseases. When gene-environment interactions alter the epigenetic state of the genome, they may affect the incidence of diseases with long latencies or late-stage onset, such as cancer and neurodegenerative diseases.

Relatively little research that has applied the tools of epigenetics to nutrigenomics has been conducted to date; but epigenetics is a rapidly developing field, one that has been invigorated by the sequencing of the human genome. The growing arsenal of tools and techniques available from the study of epigenetics thus offers new and revolutionary ways of studying how nutrients interact with the genome.

The Agouti Mouse Paradigm

The agouti mouse can express a number of different phenotypes. It can be yellow and obese or brown and slim. It can have a mottled yellow or a brown coat. These differences, however, are not genetic in origin. These mice are genetically identical. The differences arise from variations in the expression of the agouti gene; and coat color expression can be controlled by varying the mother’s diet before, during, and after pregnancy. The agouti allele is normally expressed only in a mouse’s skin, creating a yellow fur wherever it is expressed, but in agouti mice the gene is expressed throughout the body. In the mouse’s brain, for example,

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