共查询到20条相似文献,搜索用时 37 毫秒
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Decady and Thomas (2000, Biometrics 56, 893-896) propose a first-order corrected Umesh-Loughin-Scherer statistic to test for association in an r x c contingency table with multiple column responses. Agresti and Liu (1999, Biometrics 55, 936-943) point out that such statistics are not invariant to the arbitrary designation of a zero or one to a positive response. This paper shows that, in addition, the proposed testing procedure does not hold the correct size when there are strong pairwise associations between responses. 相似文献
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1. The distribution and location of the ciliated protozoan Lagenophrys aselli on the freshwater isopod Asellus aquaticus were studied in relation to water flow over the third pleopod surface. 2. At low densities L. aselli had a significant preference for the anterior centre of the pleopod; however, at the highest densities this preference was no longer significant. The distribution ranged from closer than random at low densities to further than random at the highest densities, and may have been a product of feeding and reproduction of L. aselli as well as the short intermoult period of the host. 3. An individual L. aselli has an effective area of both the lorica and the ciliated feeding disc. The ciliated feeding disc, when extended, may contribute to the presence of a small anterior–posterior gap being left between individuals. 相似文献
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Sascha Engelmann Corinna Zogel Maria Koczor Ute Schlue Monika Streubel Peter Westhoff 《BMC plant biology》2008,8(1):4
Background
The key enzymes of photosynthetic carbon assimilation in C4 plants have evolved independently several times from C3 isoforms that were present in the C3 ancestral species. The C4 isoform of phosphoenolpyruvate carboxylase (PEPC), the primary CO2-fixing enzyme of the C4 cycle, is specifically expressed at high levels in mesophyll cells of the leaves of C4 species. We are interested in understanding the molecular changes that are responsible for the evolution of this C4-characteristic PEPC expression pattern, and we are using the genus Flaveria (Asteraceae) as a model system. It is known that cis-regulatory sequences for mesophyll-specific expression of the ppcA1 gene of F. trinervia (C4) are located within a distal promoter region (DR). 相似文献9.
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Federico Buonanno 《Biologia》2011,66(4):648-653
It is known that the microturbellarian Stenostomum sphagnetorum, a common ciliate predator, is very sensitive against different types of toxins produced by other ciliates for chemical defense,
and consequently, it is not able to capture and ingests these ciliates. In particular, when the predator tries to attack one
of these toxin-secreting ciliates, it is forced to regurgitate the captured prey in response to the toxin discharged from
the ciliates. In this study it is shown that after repeated attacks by S. sphagnetorum against two species of toxic ciliates (Spirostomum ambiguum and Spirostomum teres), the predator acquires a behavior of prey selection that leads to the exclusion of these ciliates among the possible prey
and to the distinction between edible and inedible (toxic) ciliates. This learned behavior, which is maintained for days,
is lost only after the asexual reproduction of the microturbellarian. In addition, S. sphagnetorum learns to recognize and avoid specimens of S. ambiguum and S. teres artificially deprived of their toxins, strongly suggesting that the toxins are not exclusively associated in the prey recognition
of the microturbellarian. 相似文献
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It was shown earlier that the Mcp, Fab-7, and Fab-8 boundaries of the bithorax complex contain insulators that effectively block the enhancers of the yellow and white genes. Other boundaries have not been studied so far. The recent mapping of binding sites for the insulator protein dCTCF
in the regulatory regions of the bithorax complex genes permitted the Fab-3, Fab-4, and Fab-6 boundaries to be localized. Here, we showed that, despite the presence
of dCTCF-binding sites, fragments of the Fab-3, Fab-4, and Fab-6 boundaries do not exhibit the properties of insulators in
the model system with the yellow and white genes. Moreover, in some regions of the genome the Fab-4 and Fab-6 boundaries display the properties of silencers. 相似文献
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Surveys of ixodoid ticks were performed in Novosibirsk Province (Novosibirsk and Toguchin Districts) and in the vicinity of
Akademgorodok (Novosibirsk) in 2009–2010. The abundance and distribution of ticks were assessed in 8 types of habitats. Ixodes persulcatus (Schulze, 1930) was collected by flagging in Novosibirsk and Toguchin Districts, with the highest densities of 19 ind./km
being observed in habitats with small-leaved trees. Three species of ticks: Ixodes persulcatus, I. pavlovskyi (subspecies I. pavlovskyi occidentalis Filip. et Pan., 1998), and Dermacentor reticulatus (Fabricius, 1794) were recorded in a recreational forest of Akademgorodok. A high abundance (22 ind./km) of I. pavlovskyi was observed in pine forests subjected to considerable recreational load. The abundance of I. persulcatus was the highest in aspen-birch and birch-aspen forests. D. reticulatus was captured in pine forests and fallow lands, its abundance varying from 0.2 to 2 ind./km. 相似文献
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The permeability of ion channels for ions and substances that bind inside the pore depends on the cross-sectional area of the pore. We have constructed models of the closed, open, and desensitized α1β2γ2 GABAA receptor on the basis of known structures of both prokaryotic and eukaryotic ligand-gated channels. We employed Monte Carlo energy minimization to optimize the model structures. We have found significant pore constrictions, whose diameter depends on the functional state of the receptor in the cytoplasmic, middle, and extracellular parts of the pore-forming M2 segments. It is known that the constrictions in the middle (the 9' ring of residues) and cytoplasmic (the 2' ring of residues) parts of the M2 helices form the activation and desensitization gates of the GABAA receptor. Our computations predict that the constriction in the extracellular part of the M2 helices (the 20' ring of residues) may also serve as a gate in the GABAA receptor, whose physiological role is still unclear. Our results imply that the structures of a number of prokaryotic and eukaryotic ligand-gated channels that have been found in bacteria and lower organisms can be used for homology modeling of the pore region of the human GABAA receptor. 相似文献
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M. Scott Morrison Paul A. Cobine Eric L. Hegg 《Journal of biological inorganic chemistry》2007,12(8):1129-1139
The crystal structure of Cnx1G, an enzyme involved in the biosynthesis of the molybdenum cofactor (Moco) in Arabidopsis thaliana, revealed the remarkable feature of a copper ion bound to the dithiolene unit of a molybdopterin intermediate (Kuper et al. Nature 430:803-806, 2004). To characterize further the role of copper in Moco biosynthesis, we examined the in vivo and/or in vitro activity of two Moco-dependent enzymes, dimethyl sulfoxide reductase (DMSOR) and nitrate reductase (NR), from cells grown under a variety of copper conditions. We found the activities of DMSOR and NR were not affected when copper was depleted from the media of either Escherichia coli or Rhodobacter sphaeroides. These data suggest that while copper may be utilized during Moco biosynthesis when it is available, copper does not appear to be strictly required for Moco biosynthesis in these two organisms. 相似文献
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