Autosomal dosage compensation in interspecific hybrids of drosophila: Transcriptional activity in diploid and triploid hybrids

Transcriptional activity of a triploid-2L segment has been compared in an interspecific hybrid (I) (compound-2L of Drosophila melanogaster ♀ x D. simulans ♂) and an intraspecific hybrid (II) (compound-2L of D. melanogaster ♀ x Oregon R⁺ < ♂). The results reveal that although one of the three homologues in hybrid I has been contributed by D. simulans, the segment 21 A- 22F of 2L shows a level of transcriptional activity equal to that in hybrid II, where all the three homologues are from D. melanogaster. In the asynapsed region of 2L(21ABC) of hybrid I, the transcriptional activity of the two homologues derived from D. melanogaster is double that of the single homologue from D, simulans, and two-thirds of that of the two homologues of Oregon R⁺. The total transcriptional activity of this asynapsed region (21 ABC) in hybrid I is equal to that in hybrid II and the diploid Oregon R⁺. These results corroborate the existence of autosomal dosage compensation as proposed earlier and strongly suggest that, in contrast to dosage compensation of X-coded products, autosomal dosage compensation operates through suppression of activity per gene at the level of transcription.