CROSSES OF THE DDT-RESISTANT STRAINS OF DROSOPHILA MFFANOOASTER

Abstract

A series of crosses were made between the DDT-resistanl and the susceptible strains of Drosophila melanogaster. In all the three resistant strains studied, viz. P-81, P-107 and K-5 the resistance had a high degree of dominance over susceptibility. The dominance appears to be complete with low dosages (4y/cm2) and intermediate with high dosages (64, 512Y/cm2 ). The cases of considerable difference between reciprocal hybrids are frequent. As a rule, in these cases the maternal effect tended to prevail in F b with but one exception where the reverse relationship was observed. The inheritance of resistance in the P-107 strain was shown to be polygenic by a double backcross to a susceptible strain. It was established by the analysis of Fi and F2 that the factors of resistance in the strains P-81 and P-107 (derived from the same Poltava population but selected for resistance independently from one another) were not identical. Heterosis (i. e. a resistance higher than in either parental strain as measured by the per cent survival of females) may result from the crosses between certain resistant strains selected from different natural populations. Similar increase of the survival of females was observed in the crosses between the corresponding non-resistant control strains.