ABSTRACT
Premature chromosome condensation (PCC) was induced in Drosophila melanogaster cell hybrids, with Drosophila mitotic cells and interphase cells at different phases (G1,G1-S,S,S-G2 of the cell cycle, and from male and female, using standard cell fusion technique with polyethylene glycol (PEG). A combination of Feulgen and autoradiography was used to enhance the resolution of the PCC plates. It was possible to identify the characteristics of PCC's at G1, S and G2, and the transitory intermediate phases, which are comparable with respect to the characteristics of PCC's previously described for other species. Using the combined Feulgen-autoradiography technique it was possible to critically resolve the different phases including the transitory intermediate phases in greater detail. Analysis and comparison of results obtained from M (female) x S (female/male) and M (female) x G2 (female/male) hybrids have revealed that the X chromosome from the male could be identified as a distinct acrocentric entity which showed clear allocyclic, heteropycnotic characteristics. The results thus lead us to suggest that the X chromosome in such synkaryons is indeed early replicating as is the X chromosome of male larval salivary gland of Drosophila. The X chromosome morphology is also distinctly at an advanced stage of the cell cycle. On the basis of these findings it is concluded that X chromosome is hyperactive in the normally dividing diploid cells.