A gene co-expression network is a graph, where each gene corresponds to a node and a pair of nodes is connected by an undirected edge if their pair-wise expression similarity score is above a specific threshold. Construction of co-expression networks from gene expression datasets has become a widely used alternative to the conventional analytic methods. Large-scale gene co-expression networks have been applied, e.g. to demonstrate that functionally related genes are often co-expressed across variety of datasets and across distinct organisms.