Clonal parameters of tergite development in Drosophila

Abstract

A clonal analysis of abdominal development was carried out using chaeta (y, f^36a and jv) and trichome (mwh) cell marker mutants. The uncovering of these recessive markers in heterozygous individuals occurred after spontaneous loss of a X ring chromosome (gynandromorphs) or by somatic recombination induced at different developmental stages by 1000 r of X-ray. The minimum spot sizes resulting from preblastodermic gynandromorphs indicate that the least number of primitive analge cells is about 8. This is also the number of imaginal cells per analge present throughout the larval stages of development. Only with the onset of metamorphosis do the imaginal cells start dividing and spreading over the presumptive tergite area, each pair of bilateral anlage giving rise to a complete tergite. All the tergites studied (II–VI) behaved uniformly in the present experiments. Corresponding with the constant number of imaginal cells during the larval development there is a constant frequency of induced spots or a constant cell sensitivity to SCO. This sensitivity varies depending on the chromosome considered, being higher in the X chromosome than in the 3L chromosome arm. The data on gynandromorphs, as well as those of somatic spots, indicate that the adult tergites have an indeterminate pattern of growth. The cell determination to become trichome or micro- or macrochaeta occurs sometime during the pupal expansion of the growing imaginal cell population. Trichome- and chaeta-forming cells may then be separated to construct the adult cuticular pattern.