Cytology of aberrations induced by X-rays in oocytes of Drosophila melanogaster.

200 first-division configurations were analyzed for cytological aberrations induced by X-rays in late meiotic prophase in oocytes of Drosophila melanogaster. For the 3000 and 6000 r doses, 38 and 66%, respectively, were classified as abnormal. The aberrant divisions included displacement of the chromosomes suggesting their non-disjunction, loss of a whole chromosome, fragments and heterologous exchanges and unidentifiable aberrations. Non-disjunctional chromosomes were free of heterologous exchanges. The concept that a majority of X-ray-induced dominant lethals is due to chromosomal breakage is supported by the findings of the present study.