Fig. 3. Generic neuroblasts from the Drosophila CNS. The neuroblasts (NBs) divide in a stem-cell like fashion, giving rise to a ganglion mother cell (GMC, G) at each division. The GMCs divide to give rise to neurons (n). Although drawn symmetrically for simplicity, the GMC divisions are often asymmetric, giving rise to neurons of different types. The temporal progression of transcription factor expression in the NB specifies temporal identity in the successive GMCs and is indicated by color coding. Cas, Castor; Hb, Hunchback; Kr, Krüppel.