Bristle analysis of transgenic flies over-expressing various Da proteins in proneural clusters in vivo. A, pattern of large (macrochaete; black arrow) and small (micochaete; black arrowhead) bristles on the wild-type thorax. B, thorax of a fly with the C253-gal4 driver over-expressing Da-WT contains numerous ectopic macrochaete (black arrows) and microchaetae on the scutellum (black arrowheads; compare with A). C and D, the thorax of flies over-expressing Da-bHLH with the C253-gal4 driver contain extra macrochaete, including some that are immediately adjacent to other macrochaete (white arrowhead and insert in C), and bristles with twinned shaft/bristle cells (white arrow and insert in D). E, bristle pattern of the wild-type head. F, the head of a fly over-expressing Da-bHLH with the sca-gal4 driver contain extra bristles that are immediately adjacent to other macrochaete (white arrowhead) and bristles with twinned shaft/bristle cells (white arrows). The presence of extra macrochaetes immediately adjacent to normal macrochaetes is characteristic of defects in Notch signalling.