[Critical periods in the development of mutants in scute Drosophila melanogaster]

Thermosensitive periods of the development of germs of separate pairs of macrochaetae were studied in two lines of mutation of scute Drosophila melanogaster (y/sc4B and cs7). The experiments have revealed the following three features which had not been observed earlier in similar investigations in other mutants of drosophila: 1) change of thermosensitivity in mutants sc7 in different periods of ontogenesis; 2) different sensitivity in mutants of both lines in different critical periods of the same pair of macrochaetae; 3) discrete sensitivity of separate macrochaetae in mutants of both lines at different stages of oogenesis when there are no germs of these organs yet. The change of penetrability of the mutation of scute for scuttellar macrochaetae in mutants y/sc4B caused by the 90-minute-long heating of larvae on the 4th day of their life (critical period of development) is inherited in 15 observed generations of the maternal line. One may consider these periods of the increased thermosensitivity to be tje periods of stepwise determination of germs of separate pairs of macrochaetae.