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排序方式: 共有126条查询结果,搜索用时 31 毫秒
101.
Chaubey G Metspalu M Choi Y Mägi R Romero IG Soares P van Oven M Behar DM Rootsi S Hudjashov G Mallick CB Karmin M Nelis M Parik J Reddy AG Metspalu E van Driem G Xue Y Tyler-Smith C Thangaraj K Singh L Remm M Richards MB Lahr MM Kayser M Villems R Kivisild T 《Molecular biology and evolution》2011,28(2):1013-1024
The geographic origin and time of dispersal of Austroasiatic (AA) speakers, presently settled in south and southeast Asia, remains disputed. Two rival hypotheses, both assuming a demic component to the language dispersal, have been proposed. The first of these places the origin of Austroasiatic speakers in southeast Asia with a later dispersal to south Asia during the Neolithic, whereas the second hypothesis advocates pre-Neolithic origins and dispersal of this language family from south Asia. To test the two alternative models, this study combines the analysis of uniparentally inherited markers with 610,000 common single nucleotide polymorphism loci from the nuclear genome. Indian AA speakers have high frequencies of Y chromosome haplogroup O2a; our results show that this haplogroup has significantly higher diversity and coalescent time (17-28 thousand years ago) in southeast Asia, strongly supporting the first of the two hypotheses. Nevertheless, the results of principal component and "structure-like" analyses on autosomal loci also show that the population history of AA speakers in India is more complex, being characterized by two ancestral components-one represented in the pattern of Y chromosomal and EDAR results and the other by mitochondrial DNA diversity and genomic structure. We propose that AA speakers in India today are derived from dispersal from southeast Asia, followed by extensive sex-specific admixture with local Indian populations. 相似文献
102.
103.
Foley RA Lahr MM 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2011,366(1567):1080-1089
The abundant evidence that Homo sapiens evolved in Africa within the past 200,000 years, and dispersed across the world only within the past 100,000 years, provides us with a strong framework in which to consider the evolution of human diversity. While there is evidence that the human capacity for culture has a deeper history, going beyond the origin of the hominin clade, the tendency for humans to form cultures as part of being distinct communities and populations changed markedly with the evolution of H. sapiens. In this paper, we investigate 'cultures' as opposed to 'culture', and the question of how and why, compared to biological diversity, human communities and populations are so culturally diverse. We consider the way in which the diversity of human cultures has developed since 100,000 years ago, and how its rate was subject to environmental factors. We argue that the causes of this diversity lie in the distribution of resources and the way in which human communities reproduce over several generations, leading to fissioning of kin groups. We discuss the consequences of boundary formation through culture in their broader ecological and evolutionary contexts. 相似文献
104.
Diogo Aparecido Lopes Silva Francisco Antonio Rocco Lahr Rita Pinheiro Garcia Fausto Miguel Cereja Seixas Freire Aldo Roberto Ometto 《The International Journal of Life Cycle Assessment》2013,18(7):1404-1411
Purpose
The wood panel industry is one of the most important forest-based industries in Brazil. The medium density particleboard (MDP) is currently produced and consumed worldwide and represents about 50 % of the wood panel industry in Brazil. Unlike other regions, Brazilian MDP is produced from dedicated eucalyptus plantations and heavy fuel oil is an important energy source in MDP manufacture, which may result in a different environmental profile. This paper presents a life cycle assessment of MDP panel produced in Brazil and suggests improvement opportunities by assessing alternative production scenarios.Methods
The cradle-to-gate assessment of 1 m3 of MDP produced in Brazil considered two main subsystems: forest and industrial production. Detailed inventories for Brazilian eucalyptus production and MDP industrial production were collected as a result of technical visits to Brazilian MDP producers (foreground systems) as well as literature review (mainly background systems). The potential environmental impacts of MDP were assessed in terms of seven impact categories using CML (abiotic depletion, acidification, global warming, eutrophication, and photochemical oxidation) and USEtox (ecotoxicity and human toxicity) impact assessment methods in order to identify the main hotspots.Results and discussion
The industrial production was responsible for most of the impacts in all impact categories, except ecotoxicity (EC). The main hotspots identified were the use of heavy fuel oil (HFO) as a thermal energy source in MDP manufacture and the production of urea–formaldehyde (UF) resin used as synthetic adhesive. Glyphosate herbicide application in soil in forestry operations was the main responsible for the impacts in EC. Scenarios for HFO substitution were assessed and results showed that substituting HFO for in-mill wood residues or diesel leads to reduced environmental impacts.Conclusions
The identification of the main hotspots in the MDP life cycle can assist the wood panel industry to improve their environmental profile. Further research should focus on UF resin production in order to reduce its environmental impacts as well as the possibility of using alternatives resins. Other sources of wood for MDP production could also be investigated (e.g., pine wood and wood residues) to assess potential improvements. 相似文献105.
Recent horizontal transfer of a mariner transposable element among and between Diptera and Neuroptera 总被引:11,自引:4,他引:7
Transposable elements of the mariner family are widespread among insects
and other invertebrates, and initial analyses of their relationships
indicated frequent occurrence of horizontal transfers between hosts. A
specific PCR assay was used to screen for additional members of the
irritans subfamily of mariners in more than 400 arthropod species.
Phylogenetic analysis of cloned PCR fragments indicated that relatively
recent horizontal transfers had occurred into the lineages of a fruit fly
Drosophila ananassae, the horn fly Haematobia irritans, the African malaria
vector mosquito Anopheles gambiae, and a green lacewing Chrysoperla
plorabunda. Genomic dot-blot analysis revealed that the copy number in
these species varies widely, from about 17,000 copies in the horn fly to
three copies in D. ananassae. Multiple copies were sequenced from genomic
clones from each of these species and four others with related elements.
These sequences confirmed the PCR results, revealing extremely similar
elements in each of these four species (greater than 88% DNA and 95% amino
acid identity). In particular, the consensus sequence of the transposase
gene of the horn fly elements differs by just two base pairs out of 1,044
from that of the lacewing elements. The mosquito lineage has diverged from
the other Diptera for over 200 Myr, and the neuropteran last shared a
common ancestor with them more than 265 Myr ago, so this high similarity
implies that these transposons recently transferred horizontally into each
lineage. Their presence in only the closest relatives in at least the
lacewing lineage supports this hypothesis. Such horizontal transfers
provide an explanation for the evolutionary persistence and widespread
distribution of mariner transposons. We propose that the ability to
transfer horizontally to new hosts before extinction by mutation in the
current host constitutes the primary selective constraint maintaining the
sequence conservation of mariners and perhaps other DNA-mediated elements.
相似文献
106.
107.
Pairwise likelihood methods for inference in image models 总被引:3,自引:0,他引:3
108.
In limulus sperm an actin filament bundle 55 mum in length extends from the acrosomal vacuole membrane through a canal in the nucleus and then coils in a regular fashion around the base of the nucleus. The bundle expands systematically from 15 filaments near the acrosomal vacuole to 85 filaments at the basal end. Thin sections of sperm fixed during stages in spermatid maturation reveal that the filament bundle begins to assemble on dense material attached to the acrosomal vacuole membrane. In micrographs fo these early stages in maturation, short bundles are seen extending posteriorly from the dense material. The significance is that these short, developing bundles have about 85 filaments, suggesting that the 85-filament end of the bundle is assembled first. By using filament bundles isolated and incubated in vitro with G actin from muscle, we can determine the end “preferred” for addition of actin monomers during polymerization. The end that would be associated with the acrosomal vacuole membrane, a membrane destined to be continuous with the plasma membrane, is preferred about 10 times over the other, thicker end. Decoration of the newly polymerized portions of the filament bundle with subfragment 1 of myosin reveals that the arrowheads point away from the acrosomal vacuole membrane, as is true of other actin filament bundles attached to membranes. From these observations we conclude that the bundle is nucleated from the dense material associated with the acrosomal vacuole and that monomers are added to the membrane-associated end. As monomers are added at the dense material, the thick first-made end of the filament bundle is pushed down through the nucleus where, upon reaching the base of the nucleus, it coils up. Tapering is brought about by the capping of the peripheral filaments in the bundle. 相似文献
109.
The effects of 18-crown-6 on the synthesis of peptides catalyzed by alpha-chymotrypsin are reported. Lyophilization of the enzyme in the presence of 50 equivalents of 18-crown-6 results in a 425-fold enhanced activity when the reaction between the 2-chloroethylester of N-acetyl-L-phenylalanine and L-phenylalaninamide is carried out in acetonitrile. Addition of crown ether renders the dipeptide synthesis in nonaqueous solvents catalyzed by alpha-chymotrypsin possible on a preparative scale. The acceleration is observed in different solvents and for various peptide precursors. Copyright 1998 John Wiley & Sons, Inc. 相似文献
110.
We report here the structural determination of N-linked oligosaccharides
found on extracellular hemoglobins of the hydrothermal vent tube worm
Riftia pachyptila. Structures were elucidated by a combination of
electrospray ionization tandem mass spectrometry, matrix- assisted laser
desorption/ionization mass spectrometry, normal-phase high performance
liquid chromatography, and exoglycosidase digestion. The sugar chains were
found to consist mainly of high-mannose-type glycans with some structures
partially capped by one or two terminal glucose residues. The present study
represents the first report of the occurrence of glucose capping of
N-linked carbohydrates in a secreted glycoprotein of a metazoan.
Previously, glucose capping has only been described for a membrane-bound
surface glycoprotein from the unicellular parasite Leishmania mexicana
amazonensis.
相似文献