Patterns of incorporation of tritiated thymidine by the dorsal polytene foot-pad nuclei of Sarcophaga bullata (Sarcophagidae:Diptera).

The incorporation of tritiated thymidine into the DNA of the dorsal foot-pad nuclei of Sarcophaga bullata, during pharate adult development, was studied by scintillation counting and autoradiography. Incorporation was maximal on day 4 and showed a progressive temporal decline on days 5 to 8. Autoradiographs of chromosomal arms A1, A2 and D1, from late stages of the prolonged S period, showed discontinuous incorporation. On days 7 and 8 loci which incorporated the radio-labeled precursor were almost exclusively associated with DNA granules. DNA granules were associated with 8 specific loci in chromosomal arm A1, 10 in A2, and 8 in D1. The relationship between patterns of incorporation of tritiated thymidine and DNA granules is discussed.