9
BOOLEAN NETWORKS
9.1 INTRODUCTION
Genes are either “on” or “off.” When a gene is on, it is said to be expressed; otherwise, it is not expressed. The state of a gene is called the expression level of the gene. It is generally believed that the state of an organism is largely determined by the pattern of expression of its genes. This means that how well a cell performs its function is controlled by the level at which genes are expressed in the cell.
Many biological processes of interest, such as cell differentiation during development, aging, and disease, are controlled by complex interactions over time between hundreds of genes. Also, each gene is involved in multiple functions, which means that understanding the nature of complex biological processes requires determining the spatiotemporal expression patterns of thousands of genes. This also requires understanding the principles that allow biological processes to function in a coherent manner under different environmental conditions.
Boolean networks were introduced as discrete dynamic models originally intended to model genetic regulatory networks (GRNs). They are currently used in modeling other systems including social networks and biological networks because they can monitor the dynamic behavior of large complex systems. They are graphical models whose nodes are Boolean variables that can assume only two values denoted by 0 and 1, which correspond to the logical values “false” and “true,” respectively.
9.2 INTRODUCTION TO ...
