THE FORMATION OF SENSORY ORGANS IN DROSOP HILA

The formation of sensory organs in Drosophila involves a series of cho ices, each orle depending on a small set of genes. In a first step, sm all clusters of cells at defined positions of the ectoderm acquire the competence to form sensory organs. Within each cluster, the competenc e is progressively restricted to a single cell, the sensory mother cel l (second decision.). The type of sensory organ to be formed by the mo ther cell is then determined (third decision), The mother cell divides according to a fixed lineage, in which each daughter cell adopts its own fate (fourth decision). One of the daughter cells, the neuron, est ablishes specific connections in the central nervous system (fifth dec ision). The genetic analysis of this process illuminates the intertwin ing of genetic and cell interactions which is probably an essential pr operty of any developmental program.