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51.
52.
Efficiencies of different genes and different tree-building methods in recovering a known vertebrate phylogeny 总被引:24,自引:6,他引:18
The relative efficiencies of different protein-coding genes of the
mitochondrial genome and different tree-building methods in recovering a
known vertebrate phylogeny (two whale species, cow, rat, mouse, opossum,
chicken, frog, and three bony fish species) was evaluated. The
tree-building methods examined were the neighbor joining (NJ), minimum
evolution (ME), maximum parsimony (MP), and maximum likelihood (ML), and
both nucleotide sequences and deduced amino acid sequences were analyzed.
Generally speaking, amino acid sequences were better than nucleotide
sequences in obtaining the true tree (topology) or trees close to the true
tree. However, when only first and second codon positions data were used,
nucleotide sequences produced reasonably good trees. Among the 13 genes
examined, Nd5 produced the true tree in all tree-building methods or
algorithms for both amino acid and nucleotide sequence data. Genes Cytb and
Nd4 also produced the correct tree in most tree-building algorithms when
amino acid sequence data were used. By contrast, Co2, Nd1, and Nd41 showed
a poor performance. In general, large genes produced better results, and
when the entire set of genes was used, all tree-building methods generated
the true tree. In each tree-building method, several distance measures or
algorithms were used, but all these distance measures or algorithms
produced essentially the same results. The ME method, in which many
different topologies are examined, was no better than the NJ method, which
generates a single final tree. Similarly, an ML method, in which many
topologies are examined, was no better than the ML star decomposition
algorithm that generates a single final tree. In ML the best substitution
model chosen by using the Akaike information criterion produced no better
results than simpler substitution models. These results question the
utility of the currently used optimization principles in phylogenetic
construction. Relatively simple methods such as the NJ and ML star
decomposition algorithms seem to produce as good results as those obtained
by more sophisticated methods. The efficiencies of the NJ, ME, MP, and ML
methods in obtaining the correct tree were nearly the same when amino acid
sequence data were used. The most important factor in constructing reliable
phylogenetic trees seems to be the number of amino acids or nucleotides
used.
相似文献
53.
Nucleic acids extracted from microbial biomass without prior culturing were hybridized with probes representing four mer operons to detect genes encoding adaptation to Hg2+ in whole-community genomes. A 29-fold enrichment in sequences similar to the mer genes of transposon Tn501 occurred during adaptation in a freshwater community. In an estuarine community, all four mer genes were only slightly enriched (by three- to fivefold), suggesting that additional, yet uncharacterized, mer genes encoded adaptation to Hg2+. 相似文献
54.
The role of mer(Tn21) in the adaptation of aquatic microbial communities to Hg2+ was investigated. Elemental mercury was the sole product of Hg2+ volatilization by freshwater and saline water microbial communities. Bacterial activity was responsible for biotransformation because most microeucaryotes did not survive the exposure conditions, and removal of larger microbes (greater than 1 micromole) from adapted communities did not significantly (P greater than 0.01) reduce Hg2+ volatilization rates. DNA sequences homologous to mer(Tn21) were found in 50% of Hg2+-resistant bacterial strains representing two freshwater communities, but in only 12% of strains representing two saline communities (the difference was highly significant; P less than 0.001). Thus, mer(Tn21) played a significant role in Hg2+ resistance among strains isolated from fresh waters, in which microbial activity had a limited role in Hg2+ volatilization. In saline water environments in which microbially mediated volatilization was the major mechanism of Hg2+ loss, other bacterial genes coded for this biotransformation. 相似文献
55.
P E McKeever R L Wahl P Shakui G A Jackson L H Letica M Liebert J A Taren W H Beierwaltes J T Hoff 《The journal of histochemistry and cytochemistry》1990,38(6):815-822
To test the feasibility of primary screening of hybridoma supernatants against human glioma tissue, over 5000 combinations of hybridoma supernatants with glioma tissue, cultured glioma cells, and normal central neural tissue were screened with a new multiple-well (M-well) screening system. This is an immunoperoxidase assay system with visual endpoints for screening 20-30 hybridoma supernatants per single microscope slide. There were extensive differences between specificities to tissue and to cultured glioma cells when both were screened with M-wells and when cultured cells were screened with standard semi-automated fluorescence. Primary M-well screening with glioma tissue detected seven hybridoma supernatants that specifically identified parenchymal cells of glioma tissue and that were not detected with cultured cells. Immunoreactivities of individual supernatants for vascular components (nine supernatants), necrosis (five supernatants), and nuclei (three supernatants) were detected. Other supernatants bound multiple sites on glioma tissue and/or subpopulations of neurons and glia of normal tissue. The results show that primary screening with glioma tissue detects a number of different specificities of hybridoma supernatants to gliomas not detected by conventional screening with cultured cells. These are potentially applicable to diagnosis and therapy. 相似文献
56.
采用红外气体分析仪,于2008年10月17-19日连续3个昼夜原位监测了荷木的树干CO_2释放通量、树干温度、木质部液流密度和CO_2浓度.结果表明:树干CO_2释放通量(EA)日变化呈S形曲线,不同径级间差异显著.EA与树干温度呈显著幂函数关系(0.24Abstract: By using a Li-820 infra-red CO_2 gas analyzer, an in situ measurement of Schima super-ba stem CO_2 efflux was conducted for three consecutive days from 17 to 19 October 2008. In the meantime, the stem temperature, xylem sap efflux density, and xylem CO_2 concentration were measured. The stem CO_2 efflux had a diurnal variation of "S" pattern, and differed significantly with stem diameter. There was a significant exponential relationship between stem CO_2 efflux and stem temperature (0. 24 < R~2 < 0. 78). The temperature coefficient (b) and regression coeffi-cient (R~2) were higher at nighttime than at daytime, and the Q_(10) value ranged from 2. 01 to 2. 79. The stem CO_2 efflux correlated significantly with the xylem CO_2 concentration, and the best regression curve was cubic (R~2= 0. 48). Excluding the effects of stem temperature, the stem CO_2 efflux showed a significant negative correlation with xylem sap flux density (r =-0.462). Therefore, only using simple temperature function to estimate stem CO_2 efflux would yield a significant error, and xylem sap flux should be taken into consideration in the stem CO_2 emux estimation. 相似文献
57.
58.
Neuza M Alcantara-Neves Samuel J Badaró Mariese CA dos Santos Lain Pontes-de-Carvalho Maurício L Barreto 《Respiratory research》2010,11(1):114
Background
The elucidation of factors that trigger the development of transient wheezing in early childhood may be an important step toward understanding the pathogenesis of asthma and other allergic diseases later in life. Transient wheezing has been mainly attributed to viral infections, although sensitisation to aeroallergens and food allergens may occur at an early age. In developing countries, intestinal helminthic infections have also been associated with allergy or atopy-related disorders.Objective
The aim of this study was to explore the association of Trichuris trichiura and Ascaris lumbricoides infections with wheezing and atopy in early childhood.Study design
A cross-sectional study using a Portuguese-language ISAAC phase I questionnaire, adapted for preschool-aged children, nested in a cohort study of childhood diarrhoea, was conducted on 682 children. Two faecal samples per child were examined for the presence of intestinal helminthic infection. IgE antibodies against three allergenic preparations (Dermatophagoides pteronyssinus, Blomia tropicalis and common child food), as well as against A. lumbricoides antigens, were measured in a sub-sample of these children, whose parents allowed the procedure. Atopy was defined by the presence of levels of serum IgE antibodies ≥0.35 kU/L against at least one of the three tested allergenic preparations.Results
Active T. trichiura infection but not A. lumbricoides infection was positively associated with wheezing in the total studied children population [adjusted OR = 2.60; CI = 1.54;4.38] and in the atopic children sub-population [adjusted OR = 3.07; CI = 1.00;9.43]. The association with atopy was also positive and statistically significant only in the brute analysis [OR = 2.13; CI = 1.03;4.40]. Anti-A. lumbricoides IgE antibodies, but not current A. lumbricoides infection, were positively associated with wheezing in atopic children [adjusted OR = 2.01; CI = 1.00;4.50] and in non-atopic children [adjusted OR = 3.07; CI = 1.13;8.35] and it was also associated with atopy [adjusted OR = 7.29; CI = 3.90; 13.4]. On the other hands, reports of wheezing were not significantly associated with atopy.Conclusions
These data corroborate previous studies showing that wheezing is predominantly associated with infection in early childhood and shows that anti-A. lumbricoides IgE antibodies, but not active Ascaris infections, are associated with wheezing and atopy. Additionally, the data demonstrate that T. trichiura infection may play a role in the pathogenesis of atopic wheezing in early childhood. 相似文献59.
60.
Ubydul Haque Ricardo J Soares Magalhães Heidi L Reid Archie CA Clements Syed Masud Ahmed Akramul Islam Taro Yamamoto Rashidul Haque Gregory E Glass 《Malaria journal》2010,9(1):120