Comparative genomics of Anopheles gambiae and Drosophila melanogaster.

A sequence analysis of the genomes of Anopheles gambiae and Drosophila melanogaster reveals that Anopheles DNA is more heterogeneous and GC-richer than Drosophila DNA. The gene concentration across the Anopheles genome is characterized by low levels in the GC-poor part of the genome and a 3-fold increase in the GC-richest part; this gene density gradient is approximately half that of Drosophila. GC levels of introns and flanking sequences are correlated with GC(3) values (GC levels of third codon positions) of the corresponding genes with slopes much lower than unity; in other words, most introns and intergenic sequences are less GC-rich than the corresponding GC(3) values. These findings, which describe a compositional shift within Diptera, is of interest because of their parallels in the well studied major shift in vertebrates.