Chromosomal principle of radiation-induced F-1 sterility in Ephestia kuehniella (Lepidoptera : Pyralidae)

A dose-response analysis of chromosomal aberrations was performed in male p rogeny of gamma-irradiated males in the flour moth, Ephestia kuehniella. Fo r comparison, several female progeny from each dose level were examined. Ab errations were detected on microspread preparations of pachytene nuclei in the electron microscope and classified according to pairing configurations of synaptonemal complexes (SCs). Fragmentation and various translocations w ere the most numerous aberrations, whereas interstitial deletion and invers ion were rare. At 100 Gy, relatively simple multiple translocations were fo und. Multiple translocations showing complicated configurations occurred at 150 and 200 Gy, and their number increased with the dose. In males, the me an number of chromosomal breaks resulting in aberrations linearly increased with the dose from 8.4 to 16.2 per nucleus. In females, this value achieve d a maximum of 11.2 breaks/nucleus at 200 Gy. Three factors were suggested to contribute to the reported higher level of F-1 sterility in males than f emales: (i) survival of males with high numbers of breaks, (ii) crossing-ov er in spermatogenesis but not in the achiasmatic oogenesis, and (iii) a hig her impact of induced changes on the fertility of males than females. It wa s concluded that translocations are most responsible for the production of unbalanced gametes resulting in sterility of F-1 moths. However, F-1 steril ity predicted according to the observed frequency of aberrations was much h igher than the actual sterility reported earlier. This suggests a regulatio n factor which corrects the predicted unbalanced state towards balanced seg regation of translocated chromosomes.