Not only are DNA sequences important for gene function, but also their chromosomal environment and position within the cell nucleus. In fact, by controlling whether genes are switched on or off, the environment of genes can affect what a new cell develops into. When forming an organ like the liver or lung, many thousands of cells, all with the same subset of genes switched on, must be produced. Susan hopes to understand how new cells inherit the same pattern of environmental gene regulation as their parental cells, and thereby develop into the same cell type.