[Age specificity of the effect of 5-bromdeoxyuridine on the differentiation and puff spectrum of the salivary gland chromosomes of Drosophila virilis Sturt. I. Relationship between the viability of individuals and induction of new puffs and the period of action of 5-bromdeoxyuridine].

5-Bromodeoxyuridine (BUdR) influences the differentiation of the imaginal discs, larval viability and the chromosome puffing throughout the larval development. The differentiation of imaginal discs is more sensitive during the early 3rd instar. "cryptocephal" phenocopy appeared if the larvae were reared in the BUdR medium till the late 2nd instar. 2nd and 3rd instars are critical for the larval viability. During the period of the middle 3rd instar BUdR induced the complete spectrum of the newly forming specific puffs.