GENETICAL ANALYSIS OF A STRAIN WITH AN EXCESS OF MALES IN DROSOPHILA FUNEBRIS.

1. Brother-sister matings were made from a pair culture in the W strain of D. funebris with the sex ratio 0.502. There was a normal frequency distribution of sex ratios, showing no sex-linked lethals in the system. 2. Brother-sister matings from a pair culture of the y v sn zv stock of D. funebris with the sex ratio 0.498 gave no deviations from the normal sex ratio distribution other than should be expected from the lower viability of the mutant hemizygous males. The sex ratios in the original strains from which the mutant stock was built up were abnormal. 3. Selection for high sex ratios was made in four lines of the M strain of D. funebris. The generation mean increased significantly. Only slight differences could be found between the generations. In the series MB III b and MB IV b the balanced polygenic system was broken up and showed a spread of sex ratios from about 0.5 to nearly I.O with two obvious maxima in MB IV b, one at about 0.52 and the other at about 0.86-0.88. 4. The frequency distribution in MB IV b (fig. 3) shows that sex-linked lethals in the Y-homologous part of the X must be a part of the system. Such sex-linked lethals cannot be the only cause of the abnormal distribution, as with such a system no theoretical sex ratio values should be expected between 0.50 and 0.67. Thus there must be an interaction between the sex-linked lethals in the Y-homologous part of the X and lethals in some other part of the chromosome set. As the mechanism appears partly to be due to duplicate factors and partly to linked complementary gene actions the author has proposed the hypothesis that duplicated segments may be the cause of this phenomenon. One of the segments should lie in the X- and the Y-chromosomes and the other in one of the autosomes, or possibly be inserted in the non-homologous part of X. Homologous gene pairs would act as duplicate factors and different lethals within a segment as linked complementary factors. 5. Such a balanced system of lethals will cause many adjacent recessive mutations to retain their heterozygous condition, which Mall give a gene mechanism that combines uniformity of the species with a high degree of heritable variation. This will give a possible explanation of the accumulation of modifiers which is a characteristic of the species. [ABSTRACT FROM AUTHOR]