Parameters of the wing imaginal disc development of Drosophila melanogaster.

Abstract Using X-ray-induced somatic crossing-over, a clonal analysis of the wing disc development of Drosophila melanogaster was carried out. Individuals carrying y in the X-chromosomes, and sc J 4 ( y + ) jv and mwh in either 3 L chromosome were irradiated at different developmental stages and the induced y;mwh and jv twin clones studied with respect to their frequencies, sizes, and shapes. The results indicate that the wing imaginal disc cells grow exponentially from the beginning of the larval period up to puparium formation. A total of 15.6 divisions is necessary to complete the adult number of cells. The division rate is constant in the intermolt periods, but apparently decreases during the molt periods. The average cell cycle time for the larval period is about 8 hours 30 minutes. The cell sensitivity to SCO is more or less constant during the larval periods (0.2–0.4%). It increases during the pupal period about 4 times for the presumptive hair cells and about 5–10 times for the presumptive trichogen cells. The orientation of the mitotic spindle appears to be a major morphogenetic process. Cell divisions are preponderantly oriented along the proximodistal axis in the wing and alternating transverse and longitudinal or at random in the notum region. Clones grow in indeterminate patterns. At least two determinative events separate cell clones into different prospective developmental pathways. From the beginning of the larval period, dorsal and ventral cells do not mix over the wing margin. Forty hours before puparium formation, induced clones are able to give rise to several bristles or several hair cells but not to both in the same clone. The two differential mitoses giving rise to a bristle organ appear to be equivalent to, and to take place at the same time as, the two divisions give rise to 4 hair cells.