Autosomal dosage compensation Drosophila melanogaster strains trisomic for the left arm of chromosome 2

Drosophila melanogaster individuals trisomic for an entire chromosome arm can survive to late stages of pupal development. We have examined the levels of five enzymes whose structural genes are located on the left arm of chromosome 2 both in trisomy 2L and in diploid strains. In trisomies, three distally mapping loci showed compensated levels of expression close to that observed in the diploid strains. Analysis of electrophoretic variants of a compensated locus revealed that all three alleles are active in trisomies. The two proximally located loci displayed dose-dependent levels of expression. Therefore, at the level of the individual gene, autosomal compensation appears to be an all-or-none phenomenon. Furthermore, the compensatory response may be regionally distributed along the chromosome arm. The presence of both autosomal and sex-linked dosage compensation prompts us to speculate that there phenomenon are similar homeostatic mechanisms that modulate gene expression both in euploid and aneuploid genomes.