In order to establish a transient expression system for genes introduced into early embryos of the silkworm, Bombyx mori, we tested various promoters ligated with CAT reporter genes. The embryos into which we injected supercoiled plasmid DNA of pFb(-860/+10)CAT containing the Bombyx fibroin promoter region ligated to the CAT gene showed a reasonably high CAT activity beginning around 30 h after oviposition. This high activity was observed only when the plasmid was injected before termination of the early nuclear cleavage stage, which was about 8 h after oviposition, but not after this stage. This means that the expression of injected DNA is closely related to the presence of cleavage nuclei in early embryos. Promoters originating from insect genes, like the Bombyx sericin-1 gene, Drosophila hsp70 and Drosophila copia LTR, functioned as strong promoters in the embryos. On the contrary, promoters from mammalian virus genes, such as the SV40 early and Moloney murine leukemia virus LTR genes, functioned as weak promoters. Moreover, linearized DNAs showed no or weak activity of expression in embryos. From these results, we conclude that the silkworm embryo transient expression system is a useful tool for studying the mechanism of regulation of insect genes.

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Distorted segregation of the esterase isozyme genotypes was observed in F₂ population which was produced from a cross combination between 'Ko A' and 'Mokusekko 3' of barley varieties. After examining the segregation of esterase isozyme genotypes in B₁F₁ hybrids derived from the reciprocal backcrosses, it was made clear that the distorted segregation was caused by certation between pollens of different genotypes, independent of the female genotypes. Furthermore, the certation was controlled by a newly designated gene, Ga₂, at the locus which was linked with the multilocus, Est₁ Est₂ and Est₄, for esterase isozymes at the long arm of chromosome 3.
The distorted segregation ratios did not significantly vary among F₂ populations derived from F₁ hybrids of the same combination which were grown in different years. Mechanically mixed pollens of the parents, however, could not induce the certation.

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Fitness and its components in Drosophila melanogaster were estimated under the homozygous condition. All of these parmeters, except for egg-to-adult viability and female fecundity, were measured under interspecific competition with D. hydei. The following results were obtained: (1) Significant genetic variation was detected in fitness, productivity, adult viability, total egg-to-adult viability and female fecundity. (2) Significant correlation was obtained between fitness and productivity (r_p=0.792 for phenotypic correlation, r_g=0.945 for genotypic correlation), between fitness and total egg-to-adult viability (r_p = 0. 355, r_g=0.395), and between fitness and female fecundity (r_p=0.451, r_g=0.511). (3) There was no significant correlation between total egg-to-adult viability and fecundity (r_p= -0.046). The biological implications of the interrelationship between fitness and its components are discussed.

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