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31.
32.
越桔亚科植物化学成分研究进展 总被引:2,自引:0,他引:2
本文综述了近年来越桔亚科植物的研究进展。分别介绍了越桔属,红梅苔子属等化学成分研究的概况。 相似文献
33.
A traditional view is that sexual reproduction increases the potential for phenotypic evolution by expanding the range of genetic variation upon which natural selection can act. However, when nonadditive genetic effects and genetic disequilibria underlie a genetic system, genetic slippage (a change in the mean genotypic value contrary to that promoted by selection) in response to sex may occur. Additionally, depending on whether natural selection is predominantly stabilizing or disruptive, recombination may either enhance or reduce the level of expressed genetic variance. Thus, the role of sexual reproduction in the dynamics of phenotypic evolution depends heavily upon the nature of natural selection and the genetic system of the study population. In the present study, on a permanent lake Daphnia pulicaria population, sexual reproduction resulted in significant genetic slippage and a significant increase in expressed genetic variance for several traits. These observations provide evidence for substantial genetic disequilibria and nonadditive genetic effects underlying the genetic system of the study population. From these results, the fitness function of the previous clonal selection phase is inferred to be directional and/or stabilizing. The data are also used to infer the effects of natural selection on the mean and the genetic variance of the population. 相似文献
34.
以异源四倍体体细胞杂种为父本杂交培育三倍体柑桔植株的研究 总被引:23,自引:1,他引:22
以 3个柑桔原生质体融合而来的四倍体体细胞杂种为父本 ,与二倍体单胚性种柚子 (Citrusgrandis)以及单多胚混合型品种“华农本地早”桔 (C.reticulata)有性杂交 ,授粉后 90 d,发现种子干瘪 ,大部分种子的胚败育。将干瘪种子在 MT附加 1mg/L GA3 或 50 0 mg/L麦芽浸出物的培养基中 ,经培养抢救 ,有 2 5.6%的种子萌发成苗或继续进行胚的生长 ,后者进一步诱导能形成丛芽 ,经试管嫁接或诱导生根形成完整植株。共获得 6个组合 73棵完整植株 ,染色体数检查表明 ,2 0株为三倍体 (2 n=3x=2 7) ,32株为二倍体 (2 n=2 x=18) ,8株为非整倍体 ,其它 13株还有待于进一步检查。 相似文献
35.
Summary The ring- opening polymerization of - caprolactone catalyzed by a neutral protease from Bacillus subtilis has been studied in acetone, heptane solvents or in the absence of the solvent at 50°C. The lower oligomeric product containing mainly cyclic pentamer and tetramer was identified after 10 days in heptane. 相似文献
36.
Combinatorial interplay of promoter elements constitutes the minimal determinants for light and developmental control of gene expression in Arabidopsis. 总被引:6,自引:0,他引:6
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Higher plants are able to integrate environmental and endogenous signals to regulate gene expression for optimal development. To define the minimal sequence requirement sufficient to integrate light and developmental signals in controlling promoter activity, we carried out a systematic analysis of the roles of four well-conserved 'light-responsive elements (LREs)' common to many nuclear-encoded photosynthetic genes. A gain-of-function assay using basal promoter-reporter fusions in stable transgenic Arabidopsis was employed to demonstrate that pairwise combinations of the LREs, but not the individual elements alone, can confer light-inducible expression to the reporter gene independently of the basal promoter context and the light-triggered morphological changes. The activity of the synthetic promoters with the paired LREs can be modulated at least by the phytochrome system. Further, those synthetic light-regulated promoters confer a photosynthetic cell-specific expression pattern and respond to the chloroplast development state. Our data suggest that distinct combinatorial interactions of LREs can serve as minimal autonomous promoter determinants which integrate light and developmental signals and modulate promoter activity. 相似文献
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38.
Excess amino acid polymorphism in mitochondrial DNA: contrasts among genes from Drosophila, mice, and humans 总被引:13,自引:3,他引:10
Recent studies of mitochondrial DNA (mtDNA) variation in mammals and
Drosophila have shown an excess of amino acid variation within species
(replacement polymorphism) relative to the number of silent and replacement
differences fixed between species. To examine further this pattern of
nonneutral mtDNA evolution, we present sequence data for the ND3 and ND5
genes from 59 lines of Drosophila melanogaster and 29 lines of D. simulans.
Of interest are the frequency spectra of silent and replacement
polymorphisms, and potential variation among genes and taxa in the
departures from neutral expectations. The Drosophila ND3 and ND5 data show
no significant excess of replacement polymorphism using the
McDonald-Kreitman test. These data are in contrast to significant
departures from neutrality for the ND3 gene in mammals and other genes in
Drosophila mtDNA (cytochrome b and ATPase 6). Pooled across genes, however,
both Drosophila and human mtDNA show very significant excesses of amino
acid polymorphism. Silent polymorphisms at ND5 show a significantly higher
variance in frequency than replacement polymorphisms, and the latter show a
significant skew toward low frequencies (Tajima's D = -1.954). These
patterns are interpreted in light of the nearly neutral theory where mildly
deleterious amino acid haplotypes are observed as ephemeral variants within
species but do not contribute to divergence. The patterns of polymorphism
and divergence at charge-altering amino acid sites are presented for the
Drosophila ND5 gene to examine the evolution of functionally distinct
mutations. Excess charge-altering polymorphism is observed at the carboxyl
terminal and excess charge-altering divergence is detected at the amino
terminal. While the mildly deleterious model fits as a net effect in the
evolution of nonrecombining mitochondrial genomes, these data suggest that
opposing evolutionary pressures may act on different regions of
mitochondrial genes and genomes.
相似文献
39.
40.
HAU3是寄主范围很广的放线菌噬菌体。Southern杂交实验表明,HAU3可以整合到吸水链霉菌应城变种10-22和变铅青链霉菌66的突变体ZX1的染色体中,形成溶原,其溶原菌自发释放HAU3,不受热激和紫外线照射的诱导。通过比较HAU3衍生噬粒pIJ8300的DNA酶切片段在加热前、后电泳带谱的区别,将HAU3的cos位点在pIJ8300的图谱上得到了定位。还利用Southern杂交的方法定位了HAU3与宿主形成溶原时附着位点(attP),并利用脉冲电泳技术定位了在变铅青链霉菌ZX7和吸水链霉菌应城变种10-22中形成溶原的附着位点(attB)。这些信息均有利于以HAU3为基础的载体的发展和优化。 相似文献