Whereas the term “genome” refers to the entire DNA sequence of an organism (three billion letters of it for humans), the epigenome refers to the entire pattern of epigenetic modifications across all genes, including methyl DNA tags, methyl histone tags, acetyl histone tags and other chemical tags that we have not mentioned, in each cell type of an organism. This represents an almost unimaginable amount of information, dwarfing even the human genome project. Nevertheless, knowledge of the epigenome is essential to fully answer some of the biggest questions in biology such as: how do we develop from a ball of identical cells into a whole organism? why do we age? and how can we better understand diseases such as cancer? Not surprisingly then, epigenetics and the epigenome is a big area of research. Some of the research in this field is encompassed by the ENCODE (Encyclopedia of DNA Elements) project, an ongoing venture to identify patterns of epigenetic tags in many different types of cells for the entire human genome (http://genome.ucsc.edu/ENCODE/).
The ENCODE project is sometimes likened to the Large Hadron Collider or LHC in Switzerland. The LHC is the largest piece of scientific equipment ever built and the experiments physicist conduct with it aim to probe the fundamental details of the matter that makes up our Universe. Although biologists don’t have (or need) such a spectacular piece of kit for their research, the effort to examine the intricacy of the human epigenome has been likened to the LHC project because of its scale, complexity and the amount of information being created.
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