Host: The Japan Radiation Research Society
Co-host: Asian Association for Radiation Research
Theoretically translocations and dicentrics should be induced by radiation equally. However, most papers have reported that translocations are observed slightly more often than dicentrics after exposure to radiation.In order to learn the reason why translocations are induced more than dicentrics, induction rates of dicentrics and translocations involving chromosomes 2 and 4 in peripheral lymphocytes irradiated with X-rays at a dose of 3 Gy were examined using conventional Giemsa staining method and painting method.A total of 228 reciprocal exchanges detected in 982 metaphases were classified into three groups according to the break points of the original chromosomes. The incidence of both acentric fragments being larger than half of the original chromosome was only seven (3%), and did not contribute significantly to induction rates. When the broken acentric fragments of two affected chromosomes were smaller than half of the original chromosomes, which was found in 175 (77 %) of the rearrangements, the induction rates of dicentrics and translocations were about the same (86:89). But if the sizes of the broken segments were unequal in both chromosomes (one with a larger acentric part and the other with a smaller acentric part), the yield of dicentrics was significantly lower than that of translocations (16:30).It was found that preferential reduction of dicentrics in reciprocal exchanges originated from the heteromorphic size of broken chromosomes in the last combination. The mechanism of this preferential reduction is unknown.