Abstract
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.