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11.
We used simulated data to investigate a number of properties of maximum-
likelihood (ML) phylogenetic tree estimation for the case of four taxa.
Simulated data were generated under a broad range of conditions, including
wide variation in branch lengths, differences in the ratio of transition
and transversion substitutions, and the absence of presence of
gamma-distributed site-to-site rate variation. Data were analyzed in the ML
framework with two different substitution models, and we compared the
ability of the two models to reconstruct the correct topology. Although
both models were inconsistent for some branch-length combinations in the
presence of site-to-site variation, the models were efficient predictors of
topology under most simulation conditions. We also examined the performance
of the likelihood ratio (LR) test for significant positive interior branch
length. This test was found to be misleading under many simulation
conditions, rejecting too often under some simulation conditions. Under the
null hypothesis of zero length internal branch, LR statistics are assumed
to be asymptotically distributed chi 2(1); with limited data, the
distribution of LR statistics under the null hypothesis varies from chi
2(1).
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12.
Resistance of tomato infected with cucumber mosaic virus satellite RNA to potato spindle tuber viroid 总被引:1,自引:0,他引:1
Tomato (Lycopersicon esculentum cvs Rutgers and Lichun) plants were firstly pre-inoculated either with a cucumber mosaic virus (CMV) isolate containing satellite RNA (CMV-S52) or with a CMV isolate without satellite RNA, and then challenged 14 days later with a severe strain of potato spindle tuber viroid (PSTVd). Also, tomato plants transformed with CMV satellite cDNA and non-transgenic control plants were directly inoculated with PSTVd. Protection effects were assessed by the observation of symptoms and by assay of PSTVd accumulation in tomato plants using return polyacrylamide gel electrophoresis and silver staining. The results indicated that the satellite-transgenic plants and plants pre-inoculated with CMV-S52 showed much milder symptoms of PSTVd infection than the respective control plants. The concentration of PSTVd RNA in the satellite-transgenic plants and CMV-S52 pre-inoculated plants was reduced to about 0.02–0.03 of the controls. PSTVd infection did not increase the amount of satellite ds-RNA in plants. It is concluded that the plant resistance to PSTVd is induced by the presence of satellite RNA rather than the CMV infection. It is suggested that as there is considerable sequence similarity between satellite RNA and PSTVd, base pairings may be a cause of reduction of both symptoms and the accumulation of PSTVd. 相似文献
13.
A Bonnet PO Frappart P Dehais G Tosser-Klopp F Hatey 《Reproductive biology and endocrinology : RB&E》2006,4(1):35-11
FSH, which binds to specific receptors on granulosa cells in mammals, plays a key role in folliculogenesis. Its biological
activity involves stimulation of intercellular communication and upregulation of steroidogenesis, but the entire spectrum
of the genes regulated by FSH has yet to be fully characterized. 相似文献
14.
The community composition and the factors affecting seasonal and interannual dynamics of zooplankton in Lake Bosumtwi were studied biweekly at a central index station during 2005 and 2006. The lake zooplankton community was species poor. Mesocyclops bosumtwii was numerically superior seasonally and interannually and was endemic to the lake. Minor constituents included Moina micrura, six rotifer species (except for Hexarthra intermedia) and Chaoborus ceratopogones larvae. Low variance of cyanobacteria-dominated phytoplankton biomass underlined stable zooplankton community structure. Emergence of rare species of rotifers occurred seasonally. The climatic signature on the lake’s stratification and mixing regime was strongly influenced by atmospheric temperature, but weakly by wind strength, because of sheltering of the lake by high crater walls. Increasing mixing depth entrained high TP concentrations from below the thermocline seasonally, but reflected poorly in the phytoplankton biomass behaviour. Total zooplankton abundance did not differ seasonally, but varied markedly from year to year in its timing and magnitude. Herbivores were squeezed between food limitation and high predation pressure from Chaoborus all year round. The low fish planktivory (high fishing pressure) on Chaoborus may create a trophic bottleneck restricting energy transfer efficiency from zooplankton to fish. 相似文献
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16.
Serum from 88 pregnant sows and gilts was sampled 24 and 28 days after their first insemination or mating day. The oestrone sulphate (E1S) concentration in the samples was assessed with a commercially available radioimmunoassay kit modified for use with swine serum. The first aim was to test whether it was possible to predict litters of total number <10 piglets at term. The second aim was to compare the use of day 24 or day 28 samples, or of both, in this prediction. 相似文献
17.
Bioenergy crops currently provide the only source of alternative energy with the potential to reduce the use of fossil transportation fuels in a way that is compatible with existing engine technology,including in developing countries.Even though bioenergy research is currently receiving considerable attention,many of the concepts are not new,but rather build on intense research efforts from 30 years ago.A major difference with that era is the availability of genomics tools that have the potential to acceler... 相似文献
18.
Does host‐plant diversity explain species richness in insects? A test using Coccidae (Hemiptera) 下载免费PDF全文
1. The megadiverse herbivores and their host plants are a major component of biodiversity, and their interactions have been hypothesised to drive the diversification of both. 2. If plant diversity influences the diversity of insects, there is an expectation that insect species richness will be strongly correlated with host‐plant species richness. This should be observable at two levels (i) more diverse host‐plant groups should harbour more species of insects, and (ii) the species richness of a group of insects should correlate with the richness of the host groups it uses. However, such a correlation is also consistent with a hypothesis of random host use, in which insects encounter and use hosts in proportion to the diversity of host plants. Neither of these expectations has been widely tested. 3. These expectations were tested using data from a species‐rich group of insects – the Coccidae (Hemiptera). 4. Significant positive correlations were found between the species richness of coccid clades (genera) and the species richness of the host‐plant family or families upon which the clades occur. On a global scale, more closely related plant families have more similar communities of coccid genera but the correlation is weak. 5. Random host use could not be rejected for many coccids but randomisation tests and similarity of coccid communities on closely related plant families show that there is non‐random host use in some taxa. Overall, our results support the idea that plant diversity is a driver of species richness of herbivorous insects, probably via escape‐and‐radiate or oscillation‐type processes. 相似文献
19.
PO TIEN XIUHUA ZHANG BINGSHENG QIU BINGYI QIN GUSUI WU 《The Annals of applied biology》1987,111(1):143-152
Two virus-protecting strains, S51 and S52, were obtained for the control of cucumber mosaic virus (CMV) by local lesion selection after adding satellite RNA to the RNA genome of CMV. Both were found to protect pepper plants against a virulent strain of CMV under greenhouse and field conditions. Results from 14 localities in China indicated that the use of protective strains decreased the disease index by 21.6% to 82.8% and increased fruit yields by 10.8% to 55.6%. The host reactions and safety of S51 and S52 were tested, and the effects of the strains on plant growth were also investigated. Possible mechanisms of control of CMV-caused plant diseases by mild strains are discussed. 相似文献
20.
Biological control agents (BCAs) composed of attenuated cucumber mosaic (CMV) and its satellite RNA for controlling CMV diseases were found to induce plant resistance to a number of fungal diseases. Tests conducted in both the field and greenhouse showed evident protective effects against fungal infections by the BCAs. Artificial inoculation with a fungal spore suspension using BCA-treated plants, satellite transgenic plants and plants infected with CMV alone indicated that the resistance to fungi was induced by the virus infection, not by the presence of satellite RNA. 相似文献