Figure 1.
Gene coexpression networks. a) The expression profile of a gene i (Gi) can be represented as a row vector with dimensions (n) equal to the number of tissues (28); all profiles taken together yield an m × n gene expression matrix (X) where m = the number of genes (9,105), n = the number of tissues (28) and the expression value of Gi in tissue j is represented as xij [45]. b) Gene expression vectors can be compared using a number of different similarity (distance) measures such as the Pearson correlation coefficient (r). Genes (nodes) are connected by an edge if their vectors are sufficiently similar (e.g. r ≥ 0.7). A relatively tightly linked cluster (subgraph) of coexpressed genes is shown. c) Visual representation of the expression patterns of the genes in this cluster underscores their similarity. Color scale based on log2 (Gij/median Gi1...Gin).