The link between dosage compensation and sex differentiation in Drosophila melanogaster.

The rate of 3H-uridine incorporation into X-chromosome and autosomal RNA was measured as an indicator of relative transcription activity in larvae carrying various Sxl mutant alleles. Hyperactivity of X chromosomes was found in heteroallelic Sxlf#1/Sxlfhv#1 and homozygous Sxlf#2 female larvae. Sxlfhv#1 homozygotes. Sxlf#1/Sxl+ heterozygotes, heteroallelic X chromosome transcription. Except for Sxlf#ba, there is a correlation between the viability of the mutants and the degree to which X-chromosomes activity is elevated. Male larvae carrying the dominant male-specific lethal mutation SxlM#1 displayed X chromosomes only half as wide as those of control larvae. However, it could not be determined whether this property is the result of a lower transcription rate of underreplication of the mutated X chromosomes. The results demonstrate that the Sxl gene plays an important role in controlling X-chromosome activity. The relationship among the various genes known to act in sex differentiation and dosage compensation is discussed.