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

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Abstract
D. melanogaster individuals trisomic for an entire chromosome arm can survive to late stages of pupal development. The levels of 5 enzymes [phosphoglycerate kinase, .alpha.-glycerol-3-phosphate dehydrogenase, cytoplasmic malate dehydrogenase, alcohol dehydrogenase and dopa decarboxylase], the structural genes of which are located on the left arm of chromosome 2, were examined both in trisomy 2L and in diploid strains. In trisomies, 3 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 3 alleles are active in trisomies. The 2 proximally located loci displayed dose-dependent levels of expression. At the level of the individual gene, autosomal compensation appears to be an all-or-none phenomenon. 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 these phenomenon are similar homeostatic mechanisms that modulate gene expression both in euploid and aneuploid genomes.