AbstractAcute doses of 250 and 500r produced chromosomal aberrations in practically all treated males of the fleabeetle Omophoita cyanipennis. Spermatogonia were unaffected. In spermatogenesis, first aberrations at M I became recognizable four to six hours after radiation. Although presumably induced in a later phase than the gaps, the translocates reached their M I peak simultaneously with the gaps, about 24 to 50 hours after radiation. This is due to a marked delay in development of the cells radiated during the diffuse stage. The latest prophase effects manifested at M I were sticky interchromosomal contacts and interchanges of lateral loops of coiled chromonema (= "subchromatid exchanges''). Both gap and translocale yields increased by dose; 3000 and 12000r produced unanalyzable "pulverization" and clumping of chromosomes. The long sex chromosomes are the most probable exchange partners for any chromosomes. Interautosomal exchanges comprised only 6.8 percent of all exchanges. Aberrations caused irregular chromosome segregation and fragments both at A I and A II, resulting in undersized and supernumerary spermatid nuclei, and a great variation of chromatin content even in those nuclei that had a normal appearance.
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