Genetics of inbred Drosophila melanogaster. XXIV. Effects on the strength of the M-type.

Several branches with genome from either of two inbred lines of Drosophila melanogaster, introduced into various sources of cytoplasms, were used in tests of the strength of the M-type. In contrast to the conventional tests of dysgenesis, we examined primary non-disjunction and chromosome loss in successive broods from M/P hybrid females. In broods from the 2nd week of egg-laying, there were increased frequencies of X0-males and a strong depression of fertility. There were no indications of cytoplasmic influence on the M-type. In a third line with the same cytoplasm as in a couple of the above mentioned ones, there was a lower effect on chromosome loss and on fertility. Crosses between different genotypes, but with the same source of cytoplasm, suggested a delayed genic influence in maternal inheritance. Tests of recombination in the X-chromosome indicated a gradual depression from the mid part to the distal end. There seemed to be no genic effect on the depression of recombination. It is suggested that there are pleiotropic effects of the P-factors and that the response to the various processes could be under both genic and cytoplasmic control in the M-type females.