Radiation induced tandem duplications in Drosophila melanogaster.

T H I S paper reports the successful induction by X rays of two tandem direct duplications for the lozenge region of the X chromosome of Drosophila. Numerous tandem direct duplications (ABAB) of spontaneous origin are now known in Drosophila: Bar, STURTEVANT (1925), MULLER, PROKOFYEVA-BELGOVSKAYA and KOSSIKOV (1936) and BRIDGES (1936); Hairy wing, DEMEREC and HOOVER ( 1939) ; Dp (2: 2) Star, LEWIS (1 941 ) ; Confluens, SCHULTZ ( 1941 ) ; Abruptex, SCHULTZ (in MORGAN, SCHULTZ and CURRY 1941); Beadex, GREEN (1953); and Dp(l:l)white, GREEN (1961), JUDD (1961), RASMUSON (19651, and LEWIS (unpublished). Such duplications are generally believed to arise as the result of nonhomologous exchange between homologous chromosomes. In two cases, Dp (2: 2)s and Dp( 1 : 1 ) w, the origin of the duplication has indeed been shown to be associated with a crossover between homologous chromosomes. SLIZYNSKA ( 195 7) showed cytologically that tandem duplications are induced when male larvae are treated with formaldehyde. A tandem duplication for the bithorax region (89D-E) has been deliberately induced by X-raying diploid meiotic stages of the female (LEWIS, personal communication) . Recently, THOMAS and ROBERTS (1966) report the induction of a second chromosome (26A-28E) tandem direct duplication in experiments designed to study rearrangements induced in oocytes. Tandem direct duplications have been detected in a variety of ways: (1 ) The mutant phenotype associated with the Bar, Hairy wing and the Beadex duplications was the basis for their original detection; (2) SLIZYNSKA, and THOMAS and ROBERTS detected tandem direct duplications cytologically by examining the salivary gland chromosomes of individuals suspected of possessing chromosome aberrations; (3) in the case of the white and bithorax duplications, partial complementation between pseudoallelic mutants was the basis for the detection of the duplications. The third or complementation method of detecting duplications was the one of choice for the lozenge (Zz) region. I t will be described more fully below. Since duplications provide valuable tools for studying gene dosage relationships, it seemed desirable to develop them for the Zz pseudoallelic series.