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. Author manuscript; available in PMC: 2015 Jan 1.
Published in final edited form as: Genes Brain Behav. 2013 Dec 10;13(1):13–24. doi: 10.1111/gbb.12106

Figure 1. Summary of molecular, cellular, tissue and technical regulatory sources of observed gene-gene correlations/coexpression links.

Figure 1

Various biological activities (depicted in outer shapes) can influence the expression of two or more genes and yield correlated expression patterns, denoted as “coexpression links”. Hence coexpression links reflect the converging influences of these genetic, biochemical and environmental factors, and are thus informative of the biological state of an individual. The relative proportion of links from these various sources (depicted by small arrows) has not been surveyed in a consistent experimental system, and may vary for each gene. Furthermore, technical and cell-type variability can easily generate correlated expression patterns which are indistinguishable from “biological” sources of coexpression, such as epigenetic regulation. Therefore, when interpreting coexpression networks, it is helpful to separate gene-gene correlations with likely biological origins versus those which are related to overarching technical factors such as batch effects.