An analysis was made of the roles of the genes hedgehog , patched , dpp and wg in the development of the three primordia that form the genital disc. The morphogenetic alterations produced by ectopic expression of hh mimic a lack of ptc function. Both genetic conditions cause derepression of dpp and wg . Some of these alterations are explained by the mutual repression of wg and dpp . Cell proliferation refers to the capacity of each genital primordium to grow or to be kept in the repressed state.
Sexual differentiation refers to the type of adult structure formed by each genital primordium.
It is proposed that the control of cell proliferation in the male and female genitalia requires the concerted action of Abd-B and doublesex , either directly or indirectly, through the expression of the genes dpp and wingless . Thus, in female genital discs, the repressed male primordium does not express dpp whereas the repressed female primordium of the male genital discs expresses a reduced level of dpp . This reduced level seems to be insufficient to stimulate cell growth. The genes dpp and wg , however, do not participate in the sexual differentiation process, which depends on sexual cytodifferentiation genes. Very little information is available about gene expression during the larval period, a developmental interval critical to the formation of the adult.