X-ray induction of chromatid interchanges is somatic cells of Drosophila melanogaster: variations through the cell cycle of the pattern of rejoining.

The relative frequencies of X-ray-induced symmetrical and asymmetrical chromatid interchanges were analysed as a function of the cell cycle in somatic cells of Drosophila melanogaster. In exchanges between autosomes, during the S phase, a clear prevalence of asymmetrical rejoining was observed. Later, this prevalence became reduced as the cell approached mitosis. On the other hand, in the exchanges between X-chromosomes in the females there were no significant variations in the type of rejoining through the cell cycle, there being a slight but consistent preference for symmetrical rejoining. These data are discussed in relation to the hypothesis proposed by Olivieri et al. [12] on the organization of the chromosomal sub-units in the interphase nucleus.