The transmission process of Sex Ratio Organisms (SROs) into oocyte during oogenesis in Drosophila melanogaster was studied by electron microscopy. SROs break through a tunica propria, a non-cellular membrane surrounding the egg chamber, and move toward oocytes passing through the intercellular space of the follicle cell layer at previtellogenic stages. After reaching at the surface of an oocyte, they are incorporated into the ooplasm by pinocytosis with progress of vitellogenesis. By the final stages of oogenesis, most SROs become infolded in intracellular vesicles and yolk granules followed by transfer to the interior of the oocyte.

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A detailed examination of the developmental features of abnormal formation of pole cells and a functional analysis of the germ plasm of gs(1)N441 embryos were carried out. The germ plasm is morphologically normal. Embryos in which cleavage nuclei show retarded migration to the posterior pole do not form pole cells. Pole cells, following formation, are abnormally segregated and then intermingled between the blastoderm cell layer but retaining normal morphology and differentiating into functional germ cells. The results of cytoplasmic transplantation experiments indicate the autonomous segregation ability of the mutant polar plasm to form pole cells to possibly be affected.

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In our previous study, a culture system was developed to establish cell lines from dissociated imaginal discs of Drosophila melanogaster (Ui et al., 1987). Under the culture conditions employed, each kind of disc showed a unique profile in primary cultures. Some of the cell aggregates formed in in vitro culture of 3 to 6 weeks were capable of differentiating into adult structures in the metamorphosing host. The ratio of aggregates with this ability, however, was different according to the particular kind of imaginal disc and appeared correlated to the efficiency of cell line establishment.

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Drosophila teissieri and D. yakuba are two closely related species within the melanogaster species subgroup. They both live sympatrically in the Ivory Coast but in different places the ratio of their abundance is strikingly reversed. Alternative smooth or stepped cline of fecundity is observed in D. teissieri and D. yakuba respectively via an altitudinal transect in the Ivory Coast including lowland savannas of Lamto and various elevations and habitats (rainforest versus high-altitude grassland) on Mt Nimba. Crosses of parents of similar origin and, hence, altitude versus crosses of parents of different origin were conducted in order to assess the genetic basis of the differences observed. Allopatric pairs gave intermediate fecundities compared to either relevant sympatric pairs. Some cases of heterosis are observed that are dependent of the direction of cross. Fecundity uniquely and gradually increases with altitude irrespective of the habitat in D. teissieri while decreases, although with a strong stepwise inverse shift due to dramatic habitat change, in D. yakuba.

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Electrophoretic analyses of 19 loci affecting 12 enzymes in 17 Nepali and 11 Indian populations of common buckwheat were conducted by horizontal starch gel electrophoresis. Most of the populations were polymorphic at the loci Adh, Dia-2, Got-2, Mdh-1, Mdh-3, Pgm-2, 6-Pgdh-1 and Sdh-1 and some populations were also polymorphic at the Got-1 and Gdh loci. The populations from Nepal and West Bengal maintained slightly more variability than the average of other outcrossing annual plant species. The percentage of polymorphic loci was 39.5% and the average heterozygosity was 0.133. No distinct local differentiation was found among these populations. They had similar genetic constitutions with the populations from southern China. However, distinct allelic frequencies at some loce were observed in Almora and Rishikesh, both in Uttar Pradesh, India. The Kashmirian populations had less genetic variability and they were quite different from the others. They had lost the variant alleles at the loci Adh, Dia-2, 6-Pgdh-1 and Pgm-2, probably during the spread of cultivation. The processes that might have led to the prsent geographical pattern of allozyme variability are discussed.

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The amount of chlorophyll-deficient and other detrimental recessive mutants concealed in a cultivated buckwheat population was estimated for 17 populations from different parts of the world, by conducting more than 3000 sib crosses. The following types of abnormalities were found in cotyledons; albino 0.2%, yellow 3.4%, pale yellow 5.2%, pale green 7.5%, variegated 1.0%, morphological 3.5% and others 2.0% on the average. The frequency of each type did not vary so much among the populations and it coincided well with the frequency previously observed in the Japanese populations. Each type was also found in the foliage leaves at about 2/3 of the frequencies in cotyledons. No case of polymorphism of chlorophyll-deficient or other detrimental mutants has been found so far. These data confirmed the conclusions given by Ohnishi (1982); most of the detrimental mutants appear to be maintained in a population at very low frequency by mutation-selection balance; cases of balanced polymorphism are extremely rare, if they exist at all, in cultivated buckwheat populations.

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