Mutation Research, 126 (1984) 245-250 245 Elsevier MTR 03850 Induction of male recombination in Drosophilamelanogaster by chemical treatment M.D. Ferrrs, P. Alba, N. Xamena *, A. Creus and R. Marcos ** Departamento de Gendtica, Facultadde Ciencias, Universidad A utbnoma de Barcelona, Bellaterra (Spain) (Received18 January 1983) (Revisionreceived7 December1983) (Accepted 12 December1983) Summary Acridine orange (AO), ethidium bromide (EB), ethyl methanesulfonate (EMS) and 8-ethoxycaffeine (EOC) were fed to larvae of Drosophila melanogaster in order to test their capacity for the induction of meiotic recombination in males. Our results show that AO and EB increase significantly the male recombination frequencies. No relationship between chromosome breakage ability and male recombination induction was found since EMS and EOC, two effective chromosome-breaking agents, were unable to increase the male recombination. Morgan (1912, 1914) first reported the absence of crossing-over in Drosophila melanogaster males and since that time, this assumption has been one of the most familiar facts in genetics. Conse- quently, the absence of meiotic recombination in the male sex became an accepted rule-of-thumb in all the breeding experiments with D. melanogaster. However, Hiraizumi (1971) found a low, but significant level of spontaneous male recombina- tion in males captured from a natural population in Southern Texas. Since then, several authors have confirmed the occurrence of male recombina- tion, albeit at frequencies much lower than in females, in males from other natural populations of D. melanogaster (Broadwater et al., 1973; Kidwell and Kidwell, 1975; Matthews and Hiraizumi, 1976; Woodruff and Thompson, 1977; Yannopoulos and Pelecanos, 1977). The most commonly considered hypothesis to describe the mechanism of the genetic basis of * Present address: Facultad de Veterinaria UAB, Bellaterra, Spain. ** To whom correspondence should be addressed. 0027-5107/84/$03.00 © 1984 ElsevierSciencePublishers B.V. spontaneous male recombination is in terms of transmissible factors. Several variants of this hy- pothesis have been postulated involving episomes (Voelker, 1974; Waddle and Oster, 1974) or viruses (Roberts, 1976). Although the male recombination can be con- sidered as a spontaneous event, the knowledge that in females crossover values could be increased by extreme temperatures (Plough, 1917) and by X-ray treatment (Mavor and Svenson, 1924) has sug- gested to several authors the possibility of induc- ing male recombination by means of physical and chemical agents: X-rays (Patterson and Suche, 1934), high temperatures (Shull and Whittinghill, 1934; Plough, 1935), formaldehyde (Sobels, 1956; Lewis, 1957) and dihydroxymethylperoxide (Sobels and Van Steenis, 1957). The purpose of this paper is to report the preliminary results on the effect of 4 different chemical agents: acridine orange (AO), ethidium bromide (EB), ethyl methanesulfonate (EMS) and 8-ethoxycaffeine (EOC) on the induction of meiotic recombination in D. melanogaster males. With ref- erence to the interaction of these compounds with