[Time of gene activity during drosophila ontogenesis. III. Temperature-sensitive period of the homeotic mutation nasobemia].

The temperature-sensitive period (TSP) was determined for the homoeotic mutation Nasobemia which causes the antenna to leg transformation in D. melanogaster. The rate of homoetic transformation was measured in the adult flies which emerged after the temperature shift from 29 to 17 degrees and vice versa applied at different larval stages. The TSP begins at 29 degrees at 63 hrs and ends at 39 hrs prior to the pupation, while at 17 degrees it begins at 216 hrs and ends at 132 hrs prior to the pupation. This means that the end of the 1 st larval instar and practically all the 2nd instar are temperature sensitive. A suggestion is put forward to the effect that the TSP corresponds to the period during which the process of abnormal determination of the imaginal disc cells takes place.