An Hsp70 promoter drives expression of a dsx cDNA, into which the female-specific dsx intron 3, the dsx regulatory element (dsxRE) and an optimal splice acceptor site (from Nrk) have been inserted; the dsx intron is inserted within the open reading frame (ORF), while the dsxRE and Nrk splice acceptor site are inserted downstream of it. This was designed to result in a complete hid protein only being expressed in females (in which the dsx intron should be excised), while in males, the hid protein produced was expected to lack the C-terminal end of the wild-type protein (due to splicing of the 5' site of the dsx intron to the Nrk splice acceptor, removing part of the ORF). However, the dsx intron is excised in both sexes.