Epigenomics is a field in which researchers chart the locations and understand the functions of all the chemical tags that mark the genome. The epigenome is a multitude of chemical compounds that can tell the genome what to do. The human genome is the complete assembly of DNA (deoxyribonucleic acid)-about 3 billion base pairs – that makes each individual unique. DNA holds the instructions for building the proteins that carry out a variety of functions in a cell. The epigenome is made up of chemical compounds and proteins that can attach to DNA and direct such actions as turning genes on or off, controlling the production of proteins in particular cells.When epigenomic compounds attach to DNA and modify its function, they are said to have “marked” the genome. These marks do not change the sequence of the DNA. Rather, they change the way cells use the DNA’s instructions. The marks are sometimes passed on from cell to cell as cells divide. They also can be passed down from one generation to the next.