Before revision:  Here we study the origin of stochasticity qualitatively in a network of two genes using stochastic simulation method and argued that stochasticity in gene expression may be a choice of cellular system for optimum output with minimum energy cost.
After revision:  Here we study the origin of stochasticity qualitatively in a network of two genes using stochastic simulation method and approximately measure the energy consumption for the gene expression process. We find that the noise in gene expression process reduces the energy cost of protein synthesis. Therefore, we argued that the stochasticity in gene expression may be a choice of cellular system for optimum output with minimum energy cost.