The correlation coefficients between adjacent alternative exons. The DNA loci and all possible transcripts for two adjacent alternative exons are shown in this graph. Lengths are not to scale. Red and green boxes depict upstream and downstream alternative exons, respectively. Blue boxes are flanking constitutive exons. The random variable u represents the upstream exon and d represents the downstream one. On the right of each transcript are corresponding observed values of (u, d). Given all the ESTs covering these two exons, the correlation between exons can be calculated as the correlation between the two random variables (see text for details).