chapter  6
Principles of Gene Regulation and Epigenetics
Pages 40

All our cells develop ultimately from the zygote; each nucleated cell in a person contains the same DNA molecules. However, only a subset of the genes in a cell are expressed, and that subset varies according to the type of cell. The global gene expression pattern of a cell dictates the form of a cell, how it behaves, and ultimately its identity-whether it will be a hepatocyte, for example, or a macrophage, or a sperm cell.