Morphogenic effects of halogenated thymidine analogues on Drosophila. VI. Causal analysis of bromodeoxyuridine...

Variations in the treatment conditions which affect the frequency of BUdR-induced morphogenic lesions in Drosophila melanogaster have been studied. By varying the concentrations of BUdR and FU, or by changing the duration of treatment, it has been demonstrated that increased incorporation of BUdR into DNA results in a concomitant increase in morphogenic lesions. A quantitative analysis of the data on BUdR-induced lesions as a function of the age of the larvae at the time of treatment indicates that an analog pulse during early larval life induces fewer, but larger lesions than a similar treatment given during later stages of development. These observations support the hypothesis that the developmental modifications are the result of genetic changes which in subsequent replication cycles of DNA are transmitted to descendant cells, and are not necessarily due to the presence of BUdR in DNA per se of cells in the developing organism.