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  • Educator Carlos Guerrero-Bosagna
  • Script Editor Eleanor Nelsen
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The question of how an adult organism unfolds after the merging of two gametes have been around since Aristotelian times. Adherents of ‘preformation’ answered this question by stating that all the components needed for the embryo to become an adult individual were already inside the gametes. 

On the other side of the spectrum, those supporting ‘epigenesis’ thought that gametes and embryonic cells needed to interact with external signals in order to generate an adult individual. This site from Stanford: Epigenesis and Preformationism provides some information on the topic.

When the genomic era arrived, Conrad Waddington, a British geneticist, wanted to explain the meaning of epigenesis with genes. He questioned ‘how genes interact with their products and the environment to bring phenotypes into being?’ By combining the term ‘epigenesis’ and ‘genetics’ he came up with a term that is now becoming highly important in all fields of biological sciences: ‘Epigenetics.’ Read more about Waddington here.

One of the main aspects of epigenetics is to see the genome as a reactive chemical entity rather than as a ‘code’ directing the development of organisms towards an adult phenotype. This is because behind the A, C, G and T letters of this so-called ‘genetic code’ there is an enormous complexity: that inherent of every chemical structure.

Just as lipids or proteins, the DNA is a molecular structure, and as such, interacts with an array of other molecular structures. These can be proteins such as histones, small fragments of RNA or simply methyl groups that attach to the DNA structure. When the interaction of these molecules with the DNA is maintained even after cell divisions then they are defined as ‘Epigenetic’ modifications. A remarkable feature of epigenetic modifications is that on one hand they can regulate genes' expression, and on the other hand they can be influenced by environmental cues.

Notably, epigenetic patterns are specific for each cell type of an individual. Therefore, in each tissue, epigenetic patterns correlate with the expression profile observed in these specific cell types. The epigenetic map of a particular cell is called the epigenome. Interestingly, each individual is composed of one genome, but of multiple epigenomes, each corresponding to one specific cell type. Interested? Watch this Nature video: Epigenome: The symphony in your cells.

A major breakthrough in epigenetic research is the ability to understand the etiology of diseases for which genetic associations have never been found or when these explain only a limited number of cases. By focusing on environmental exposures during early development, and epigenetic changes produced, now the causes and mechanisms of many diseases of common and increasing occurrence are starting to be understood. For example, now some diseases such as obesity can be explained by exposures in the womb to, for example, plastic compounds.

Recently, some evidence has even shown that environmental exposures during pregnancy can generate epigenetic disturbances and increase the rate of diseases in the offspring and descendants to come. This phenomena is called transgenerational epigenetic inheritance.

Epigenetics is the discipline that bridges environmental exposures and lifelong genome regulation. Epigenetics is rapidly changing our perception of how diseases and phenotypes emerge and prosper in populations. It is becoming increasingly evident that the interplay between environmental factors and epigenetic mechanisms will have a major impact in the health status and capabilities of individuals through their entire life, as well as on their descendants. Looking for more information about this topic? This article is a great resource: Globalization, climate change, and transgenerational epigenetic inheritance: will our descendants be at risk?