X-ray-induced chromosomal translocations were studied in mouse spermat
ogonial stem cells by meiotic analysis at the spermatocyte stage many
cell generations after induction, Using a composite DNA probe for mous
e chromosomes 1, 11 and 13, in combination with fluorescence in situ h
ybridization, the involvement of these three chromosomes in translocat
ion formation was recorded, The obtained results at various sampling t
imes ranging from 75 to 320 days after irradiation show no significant
differences in the participation pattern of the painted chromosomes i
n multivalent formation with increasing sampling time, Pooling of the
data at the different dose levels of 5 and 7 Gy indicated significant
overrepresentation of the specifically stained bivalents in translocat
ion formation, This suggests that clonal proliferation cannot be held
responsible for the observed non-randomness. Experiments with the DNA-
repair inhibitor 3-aminobenzamide showed no change in the recorded ove
rrepresentation, indicating that it is probably not the repair of lesi
ons that is causing this phenomenon but rather non-random induction.