[Active period of genes during Drosophila ontogenesis. I. Temperature-sensitive period for the spineless effect in aristapedia mutants]

The temperature-sensitive period (TSP) was determined for the spineless effect (bristle shortening) in SSa40a mutant of Drosophila melanogaster. The length of front orbital and front vertical bristles was measured at different intervals after the temperature shift from 29 to 17 degrees and vice versa. The TSP was found to last from 7 to 14 hrs during pupal development. This corresponds to the activity of the spineless-aristapedia locus during the period of isolation of bristle initial cells. The discordance between the TSP of spineless effect and that of homoeotic effect of the same gene suggests that the locus SSa40a is activated twice during development.