The development of the Drosophila genital disc

The imaginal discs of Drosophila melanogaster, which form the adult epiderm al structures, are a good experimental model for studying morphogenesis. Th e genital disc forms the terminalia, which are the most sexually dimorphic structures of the fly. Both sexes of Drosophila have a single genital disc formed by three primordia. The female genital primordium is derived from 8( th) abdominal segment and is located anteriorly, the anal primordium (10 an d 11(th) abdominal segments) is located posteriorly, and the male genital p rimordium from the 9(th) abdominal segment lies between them. In both sexes , only two of these three primordial develop to form the adult terminalia. The anal primordium develops in both sexes but, depending on the genetic se x, will form either male or female analia. However, only one of the genital primordia develops in each sex, forming either the male or the female geni talia. This depends on the genetic sex of the fly. Therefore, the genital d isc is a very good experimental model of how the sex-determination and home otic genes - which determine cell identity - interact to direct the develop ment of a population of cells into male or female terminalia. It has been p roposed that the sexually dimorphic development of the genital disc is the result of an integrated genetic input, made up by the sex-determination gen e doublesex and the homeotic gene Abdominal-B. This input acts by modulatin g the response to Hedgehog, Wingless, and Decapentaplegic morphogenetic sig nals. (C) 2001 John Wiley & Sons, Inc.