Complex genes have more intergenic DNA in D. melanogaster than in C. elegans. (a) Mean 5' flanking DNA (5'), 3' flanking DNA (3'), and total intergenic DNA (T; all ± standard error) is shown for nonredundant groups of simple genes (CDY, general RNA PolII transcription factors, ribosomal components, metabolism, and housekeeping) and complex genes (embryonic development, pattern specification, and specific RNA PolII transcription factors) in C. elegans (blue) and D. melanogaster (red). C. elegans complex genes have significantly more 5' flanking DNA than 3' flanking DNA (Wilcoxon two-sample test, p < 0.0001). The C. elegans complex group is flanked by significantly less DNA than the D. melanogaster complex group (Tukey-Kramer HSD, α = 1 × 10-4). (b) Distribution of intergenic DNA for all genes in C. elegans (blue) and D. melanogaster (red). In general, genes in C. elegans are more evenly spaced than in D. melanogaster. The largest class of genes in D. melanogaster has less than 1,000 bp of intergenic DNA separating neighboring genes, whereas the largest class in C. elegans has 1,000-2,000 bp. Thus, D. melanogaster does not have a euchromatic genome that is generally expanded with respect to C. elegans, even though it has many more genes with greater than 19,000 bp of flanking intergenic DNA.
Nelson et al. Genome Biology 2004 5:R25