Effects of Actinomycin D on Crossing over in Drosophila Melanogaster.

STUDIES on crossing over are usually designed to correlate changes in crossover values with a specific genetic or environmental condition. The lack of understanding of the primary genetic effects of chromosome rearrangements makes inferences based on the effects of these aberrations on crossing over difficult ( SUZUKI 1963b). On the other hand, extrinsic factors (temperature, radiation, chemicals) which affect crossing over result in a number of physiological changes, any of which might be the primary influence on crossing over. The work reported here is a study of the possible role of a specific molecular group in crossing over. On the basis of studies on the effects of ribonuclease (KAUFMAN, GAY and MCELDERRY 1957) and far-red radiation (KAUFMAN et al. 1962), it has been concluded that RNA is involved in the process of crossing over. Actinomycin D is an antibiotic which specifically binds to DNA and inhibits synthesis of DNAmediated RNA (dm-RNA) (REICH 1964). In order to test the role of dm-RNA in crossing over, SUZUKI (1963a) studied the effects of actinomycin D on Drosophila melanogaster females. He found a specific effect which is first detected six to nine days after treatment-crossing over was increased only in the region spanning the centromere and all other crossover regions were unaffected. This report is an extension of these observations.