Replication in Drosophila chromosomes. Part VIII. Temporal order of replication of specific sites in polytene chromosomes from 24°C & 10°C reared larvae of D. melanogaster

Abstract

D. melanogaster larvae has been grown at low (10°C) and usual (24°C) temperatures to study the effect of growth temperature of replication of specific replicating sites in polytene nuclei. In an earlier study [Mishra and Lakhotia. Chromosoma, 85 (1982) 221], we suggested that the polytene S-period in cold-reared larvae is prolonged due to a greater asynchrony in the initiation and replicating units of a nucleus, while the number of replicating units and their rate of replication remain similar. In the present study. replication of different replicating units in specific segments of X and 3L in polytene nuclei from 24 and 10°C reared larvae has been examined in detail. This analysis provides further evidence for identity of replicating units at two growth temperatures and for a greater asynchrony in replication of different sites at low growth temperature. The results also suggest that the temporal order of initiation and termination or replication of different units may vary in different nuclei within certain limits. Some aspects related to these are discussed.