Trend in mean gene size, as function of contig cutoff. This analysis is restricted to cDNAs with at least some 5′ UTR sequence, because these are more likely to be full-length. When a gene is aligned to multiple contigs, the cutoff is based on the maximum contig size. In the limiting case of a 1-Mb contig cutoff, the mean gene size is 60.0 kb or 71.9 kb, depending on whether or not we include chromosomes 20 and 22. Had we based the cutoffs on the sum of the contig sizes, instead of on the maximum, the resultant gene sizes would have been even larger (65.6 kb or 81.0 kb). The arrows indicate how large the gene size must grow for there to be no intergenic DNA, assuming 2.9 Gb of euchromatic DNA and 30,000, 35,000, or 40,000 genes.