This paper describes a novel approach to obtain co-regulated genes and the underlying genetic regulatory network. Time evolution of gene expression levels is described using a discrete time classical state space dynamical system. The state transition matrix of the model can be used to obtain the adjacency matrix of the regulatory network. Gene expression values over time can also be written as a linear combination of the eigenmodes of the state transition matrix. Based on the relative participation of the eigenmodes, co-regulation is discussed.