Average Rank Co-expression as a Function of the Separation of Gene Pairs on the Chip for Worm Muscle-expression Experiment . Co-expression is defined by the score , where is the average rank percentile of expression of gene i across several replicated array experiments. For pairs used to generate the blue curve, the individual genes in each pair are from the same chromosome. For the red curve members of each pair are from different chromosomes. The green curve is a pair distribution similar to the blue curve distribution but with randomized pair-wise chip distances.