The paradigm in which the deleterious effects of ionizing radiations are attributed to chemical alterations of DNA through energy depositions is well established.However,accumulating evidence suggests that other phenomena like heritable phenotype of genomic instability(radiation-induced genomic instability,RIGI)may also occur when cells are irradiated.The manifestation of this instability may be delayed for many cell divisions;it will then show itself in a variety of ways depending on the cell system used.Delayed lethal mutations(delayed reproductive cell death),delayed apoptosis,non-clonal cytogenetically detectable The paradigm in which the deleterious effects of ionizing radiations are attributed to chemical alterations of DNA through energy depositions is well established. Host, accumulating evidence suggests that other phenomena like heritable phenotype of genomic instability (radiation-induced genomic instability, RIGI) may also occur when cells are irradiated. The manifestation of this instability may be delayed for many cell divisions; it will then show itself itself in a variety of ways depending on the cell system used. Delaying lethal mutations (delayed reproductive cell death), delayed apoptosis, non- clonal cytogenetically detectable