Lack of an Interchromosomal Effect Associated with Spontaneous Recombination in Males of Drosophila Melanogaster

It is shown that the frequency of spontaneous male recombination in two different lines of Drosophila melanogaster (OKI and T-007) are not subject to an interchromosomal effect. Second-chromosome male recombination in these lines was not affected by heterozygosity for the multiple third-chromosome inversions In(3LR)TM3 or In(3LR)Ubx, which do affect recombination in females. It seems, therefore, that a large fraction of spontaneous recombination in males of D. melanogaster occurs by some mechanism other than that in females. We discuss the possibility that the mechanism is chromosome breakage and reunion, and that these breakage events may be caused by a microorganism. OHIO J. SCI. 78(6): 310, 1978 Contrary to previous reports (Morgan 1912, 1914), spontaneous recombination does occur in some males of Drosophila melanogaster. Many stocks of D. melanogaster that are newly derived from natural populations show male recombination when outcrossed, although at frequencies much lower than those in females (Cardellino and Mukai 1975, Henderson et at 1978, Hiraizumi 1971, Hiraizumi et al 1973, Kidwell and Kidwell 1975a, 1975b, 1976, Kidwell et al 1977, Slatko and Hiraizumi 1973, 1975, Sochacka and Woodruff 1976, Sved 1976, Thompson and Woodruff 1978a, 1978b, Voelker 1974, Waddle and Oster 1974, Woodruff and Thompson 1977, Yamaguchi 1976, Yamaguchi and Mukai 1974). For a review of this topic, see Thompson and Woodruff (1978b). It is not clear, however, by what mechanism these male recombination events occur. Do they, for example, occur by the same mechanism that produces recombination in females or by some other exchange event (possibly chromosome breakage and reunion) ? To determine Manuscript received 13 January 1978 and in revised form 21 June 1978 (#78-4). Present address: Department of Genetics, University of California at Davis, Davis, CA 95616. Present address: Department of Zoology, University of Oklahoma, Norman, OK 73019. whether male recombination occurs by the same process as in females, we can examine those parameters affecting frequencies of recombination in females, and ask whether male recombination is similarly affected. It is known that the frequency of recombination can be increased by structural heterozygosity of other nonhomologous chromosomes—termed the interchromosomal effect (for reviews, see Lucchesi and Suzuki 1968, Lucchesi 1976). In Drosophila, only spontaneous recombination in females has been tested for interchromosomal effect. It was our objective, therefore, to determine whether there is an interchromosomal effect on spontaneous recombination in males of D. melanogaster. We have observed that male recombination in two different isolated chromosome lines is not influenced by an interchromosomal effect. MATERIALS AND METHODS The mutant genes, chromosome rearrangements and wild-type chromosome lines used in this study are listed as follows (see Lindsley and Grell 1968, for detailed descriptions): aristaless {al, 2L-0.0, antenna), black (b, 2L48.0, body color), brown {bw, 2R-104.5, eye color), cinnabar (en, 2R-57.5, eye color), dumpy {dp, 2L-13.0, wing shape), veinlet (ve, 3L-0.2, short wing veins), Inversion(3LR)Third Multiple-8 (In(3LR)TM8, 3rd chromosome inversions, balancer, contains the markers y, ri, pv, sep, bx', Sb and Ser), Inversion(3LR)Ultra-