Population analysis was conducted for the adaptive superiority of sepia heterozygotes to either homozygote in Drosophila melanogaster. Four populations, which had different genetic backgrounds in the initial generations, were established. In early generations, where the magnitude of linkage disequilibrium (D of Lewontin and Kojima 1960) was large, and heterozygote superiority was seen. The frequencies of sepia homozygotes reached temporary equilibria (ca. 7-14 percent). However, as generation advanced, namely, the magnitude of linkage disequilibrium became small or disappeared, the frequency of sepia homozygotes decreased. However, in three sub-populations out of fifteen, permanent linkage disequilibrium was probably formed. Thus, intrinsic overdominance of the sepia gene was rejected. Mathematical models were set up for the explanation of the experimental data, and the necessary and sufficient conditions for the pseudo-overdominance in populations were obtained.
Collections of Drosophilidae were made by trapping each month from May to October during the period of 1956 through 1962 in the University Botanical Gardens. Drosophila auraria was found to dominate over the other species collected, showing 40.08%. Ninety-three percent of the auraria population was occupied by race A. The race A showed usually a unimodal activity with a single peak in the middle of summer. However, a bimodal activity occurred in 1958 and 1960 with a small peak in May and a large one in July or August. The frequency of females in the entire sample of this race was 48.39%. The value would have been more than fifty percent, if collections would have been made in the same way in 1959 as in the other years. Because, variations in sex-ratio were found in 1959 populations sampled from different places and lures, and at different times. There was, however, a general tendency that the frequency of females of this race was inversely related to the population activity.
1. In acid solution below pH 3.5, a Salmonella flagellum dissociates into homogeneous protein monomers called 'flagellin'. Molecular weight of a flagellin particle, estimated from its sedimentation coefficient is about 37, 000. A flagellin is composed of 15 to 17 kinds of amino acids, 272 in number. Its amino acid composition is characterized by abundance of aspartic acid and alanine and absence of tryptophan. Relative amount of each component amino acid in a flagellin differs among different Salmonella strains.