The cytoplasmically-inherited "sex-ratio" condition in natural and experimental populations of Drosophila bifasciata.

HE cytoplasmically-inherited “sex-ratio” condition (SR) has been analyzed by many workers. BUZZATI-TRAVERSO (1941) first reported “sex-ratio” females in Drosophila bilineata (=D. bijasciata) collected in natural populations in Italy. “Sex-ratio” females of the same species were found in Pavia, Italy (MAGNI 1953) and also in Asakawa, Japan (MORIWAKI and KITAGAWA 1954). Further examples of the “sex-ratio” condition have been reported in Drosophila prosaltans ( CAVALCANTI and FALCAO 1954), D. borealis (CARSON 1956), D. willistoni (MALOGOLOWKIN 1958), D. equinoxialis (MALOGOLOWKIN 1959a), D. nebulosa (POULSON and SAKAGUCHI 1960b) and D. robusta (POULSON 1966). The general features of the “sex-ratio” condition in the eight species mentioned above are as follows: (1) SR females produce offspring that consist almost entirely of daughters. (2) XY zygotes are killed in early developmental stages. (3) The SR condition is inherited only through the cytoplasm. However, there are some differences among the SR conditions originating in different species. The SR conditions in the species of the willistoni group are infective both interand intraspecifically through injection with ooplasm of SR eggs ( MALOGOLOWKIN and POULSON 195 7; MALOGOLOWKIN 1959a,b; MALOGOLOWKIN, CALVALHO and DA PAZ 1960). Also, the infectivity with hemolymph of SR females was demonstrated by SAKAGUCHI and POULSON (1960, 1963). POULSON and SAKAGUCHI (1960a, 1961) found that the infectious cytoplasmic agents responsible for the SR condition in these species are spirochaetes. On the other hand, the SR condition in D. bifasciata cannot be transferred intraspecifically by injection with abnormal ooplasm (MALOGOLOWKIN and CALVALHO 1961). The [SRI agents of D. bifasciata SR are transmittable only through injection of SR ovary homogenates, but the infectivity is very low compared with D. willistoni [SRI agents (LEVENTHAL 1968). LEVENTHAL (1968) concluded that the [SRI agents in D. bifasciata might be intracellular virus-like microorganisms. The evidence that the SR conditions are affected not only by cytoplasmic factors but by nuclear genes was demonstrated in D. prosaltam (CAVALCANTI, FALCAO and CASTRO 1958), in D. willistoni (SAKAGUCHI and POULSON 1960b; MALOGOLOWKIN 1958) and in D. paulistorum (MAMGOLOWKIN 1958). CAVALCANTI, FALCAO and CASTRO (1958) concluded that these genes would be comparable to the well-known k gene in Paramecium which acts to suppress the