Cuticles of adult male (top) and female (bottom) showing sexually dimorphic segment number. 

Engrailed (green) and sexually dimorphic Wingless (red) expression in the developing D. melanogaster abdomen.
and Evolution

Sex-specific segment elimination in the adult abdomen is a synapomorphy of the Cyclorrhaphan diptera which diverged an estimated 150 million years ago. We are investigating the genetic mechanisms that underlie segment elimination in Drosophila melanogaster in order to establish and test hypotheses about the evolution and stasis of this trait.