排序方式: 共有66条查询结果,搜索用时 328 毫秒
21.
水稻卷叶螟的田间种群包括三个种,即稻纵卷叶螟(Cnaphalocrocis medinalis),和 MarasmiaPatnalis,M.exigua。1989年雨季在菲律宾吕宋岛上两个点进行的试验共分别记录了15(内湖省)和12(中吕宋)个种的幼虫寄生性天敌,它们分别攻击寄主卵~幼虫、幼虫和幼虫~蛹期,这些寄生性天敌分属于外寄生或内寄生,单寄生或多寄生,这种生物学特征上的差异为寄生性天敌提供了降低寄主种群的广大的机会。进一步的调查显示,那些攻击低龄寄主的种类具有高繁殖力的小个体的特征,而攻击高龄寄主的种类具有较宽的寄主范围且常常发育历期较短。多数天敌寄生于2或3龄幼虫,将寄主杀死于5龄之前,优势种及寄生率随寄主密度和水稻的生长期不同而变化。 根据Hill(1972)的多样性序列指数分析指出,当以N_2为标准时,在内湖省的整个水稻生育期内始终仅有2—3个种为极优势种,其数据适于用几何或对数序列进行描述。两个点的寄生性天敌种群多样性(N_2)接近于常数3—4,均匀度(E_5)与寄主幼虫密度呈负相关。因此,幼虫的寄生作用可被认为是一个抑制并稳定水稻卷叶螟田间种群的关键因子。 相似文献
22.
王磊 《应用基础与工程科学学报》1994,(Z1)
对一般系数随机的带有相关因子的多元线性回归模型的参数进行估计。估计值是用EM算法给出的极大似然估计或约束的极大似然估计。给出了EM算法的具体公式,并利用bootstrap方法估算出这些估计值的精确度。最后通过一判别儿童总体中是否存在Catch-Up生长的例子以解释给出的方法。 相似文献
23.
Since the discovery of the hepatitis C virus over 15 years ago, scientists have raced to develop diagnostics, study the virus and find new therapies. Yet virtually every attempt to dissect this pathogen has met with roadblocks that impeded progress. Its replication was restricted to humans or experimentally infected chimpanzees, and efficient growth of the virus in cell culture failed until very recently. Nevertheless hard-fought progress has been made and the first wave of antiviral drugs is entering clinical trials. 相似文献
24.
An SNP map of human chromosome 22 总被引:35,自引:0,他引:35
Mullikin JC Hunt SE Cole CG Mortimore BJ Rice CM Burton J Matthews LH Pavitt R Plumb RW Sims SK Ainscough RM Attwood J Bailey JM Barlow K Bruskiewich RM Butcher PN Carter NP Chen Y Clee CM Coggill PC Davies J Davies RM Dawson E Francis MD Joy AA Lamble RG Langford CF Macarthy J Mall V Moreland A Overton-Larty EK Ross MT Smith LC Steward CA Sulston JE Tinsley EJ Turney KJ Willey DL Wilson GD McMurray AA Dunham I Rogers J Bentley DR 《Nature》2000,407(6803):516-520
The human genome sequence will provide a reference for measuring DNA sequence variation in human populations. Sequence variants are responsible for the genetic component of individuality, including complex characteristics such as disease susceptibility and drug response. Most sequence variants are single nucleotide polymorphisms (SNPs), where two alternate bases occur at one position. Comparison of any two genomes reveals around 1 SNP per kilobase. A sufficiently dense map of SNPs would allow the detection of sequence variants responsible for particular characteristics on the basis that they are associated with a specific SNP allele. Here we have evaluated large-scale sequencing approaches to obtaining SNPs, and have constructed a map of 2,730 SNPs on human chromosome 22. Most of the SNPs are within 25 kilobases of a transcribed exon, and are valuable for association studies. We have scaled up the process, detecting over 65,000 SNPs in the genome as part of The SNP Consortium programme, which is on target to build a map of 1 SNP every 5 kilobases that is integrated with the human genome sequence and that is freely available in the public domain. 相似文献
25.
A map of human genome sequence variation containing 1.42 million single nucleotide polymorphisms 总被引:69,自引:0,他引:69
Sachidanandam R Weissman D Schmidt SC Kakol JM Stein LD Marth G Sherry S Mullikin JC Mortimore BJ Willey DL Hunt SE Cole CG Coggill PC Rice CM Ning Z Rogers J Bentley DR Kwok PY Mardis ER Yeh RT Schultz B Cook L Davenport R Dante M Fulton L Hillier L Waterston RH McPherson JD Gilman B Schaffner S Van Etten WJ Reich D Higgins J Daly MJ Blumenstiel B Baldwin J Stange-Thomann N Zody MC Linton L Lander ES Altshuler D;International SNP Map Working Group 《Nature》2001,409(6822):928-933
We describe a map of 1.42 million single nucleotide polymorphisms (SNPs) distributed throughout the human genome, providing an average density on available sequence of one SNP every 1.9 kilobases. These SNPs were primarily discovered by two projects: The SNP Consortium and the analysis of clone overlaps by the International Human Genome Sequencing Consortium. The map integrates all publicly available SNPs with described genes and other genomic features. We estimate that 60,000 SNPs fall within exon (coding and untranslated regions), and 85% of exons are within 5 kb of the nearest SNP. Nucleotide diversity varies greatly across the genome, in a manner broadly consistent with a standard population genetic model of human history. This high-density SNP map provides a public resource for defining haplotype variation across the genome, and should help to identify biomedically important genes for diagnosis and therapy. 相似文献
26.
Clifford G. Rice 《西北部美国博物学家》2011,63(2)
Call counts and brood counts are frequently used to evaluate Ring-necked Pheasant ( Phasianus colchicus ) populations and to forecast harvest. Given the variability commonly observed in these counts, I evaluated their utility in performing these functions in the state of Washington. Pheasant harvest, call counts, and brood counts have all declined in Washington State since 1982. Power for detecting trends in call counts was higher than for brood counts, but substantial sampling was required to reliably detect even large changes in the short term (e.g., power=0.9 for a 40% decline between 2 years with 12 routes). Brood counts predicted harvest with greater precision than did call counts, but predictions were meaningful only at the statewide scale (i.e., not for counties or major river basins). This was true for predicting total harvest and relative harvest (high, medium, or low). 相似文献
27.
A diverse range of gene products are effectors of the type I interferon antiviral response 总被引:1,自引:0,他引:1
The type I interferon response protects cells against invading viral pathogens. The cellular factors that mediate this defence are the products of interferon-stimulated genes (ISGs). Although hundreds of ISGs have been identified since their discovery more than 25 years ago, only a few have been characterized with respect to antiviral activity. For most ISG products, little is known about their antiviral potential, their target specificity and their mechanisms of action. Using an overexpression screening approach, here we show that different viruses are targeted by unique sets of ISGs. We find that each viral species is susceptible to multiple antiviral genes, which together encompass a range of inhibitory activities. To conduct the screen, more than 380 human ISGs were tested for their ability to inhibit the replication of several important human and animal viruses, including hepatitis C virus, yellow fever virus, West Nile virus, chikungunya virus, Venezuelan equine encephalitis virus and human immunodeficiency virus type-1. Broadly acting effectors included IRF1, C6orf150 (also known as MB21D1), HPSE, RIG-I (also known as DDX58), MDA5 (also known as IFIH1) and IFITM3, whereas more targeted antiviral specificity was observed with DDX60, IFI44L, IFI6, IFITM2, MAP3K14, MOV10, NAMPT (also known as PBEF1), OASL, RTP4, TREX1 and UNC84B (also known as SUN2). Combined expression of pairs of ISGs showed additive antiviral effects similar to those of moderate type I interferon doses. Mechanistic studies uncovered a common theme of translational inhibition for numerous effectors. Several ISGs, including ADAR, FAM46C, LY6E and MCOLN2, enhanced the replication of certain viruses, highlighting another layer of complexity in the highly pleiotropic type I interferon system. 相似文献
28.
Sequence, structure and activity of phosphoglycerate kinase: a possible hinge-bending enzyme. 总被引:20,自引:0,他引:20
R D Banks C C Blake P R Evans R Haser D W Rice G W Hardy M Merrett A W Phillips 《Nature》1979,279(5716):773-777
The fitting of sequenced peptides to a high-resolution X-ray map of phosphoglycerate kinase has yielded the complete sequence and structure of the horse muscle enzyme. Metal ADP and ATP substrates are bound to one of the two widely separated domains in an environment that seems unsuitable for phosphoglycerate binding. The most plausible binding site for the phosphoglycerate substrate is on the other domain about 10 A from the ATP, which implies the possibility of a large scale hinge-bending of the domains to bring the two substrates together in a water-free environment for catalysis. 相似文献
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30.
The draft genome of the transgenic tropical fruit tree papaya (Carica papaya Linnaeus) 总被引:1,自引:0,他引:1
Ming R Hou S Feng Y Yu Q Dionne-Laporte A Saw JH Senin P Wang W Ly BV Lewis KL Salzberg SL Feng L Jones MR Skelton RL Murray JE Chen C Qian W Shen J Du P Eustice M Tong E Tang H Lyons E Paull RE Michael TP Wall K Rice DW Albert H Wang ML Zhu YJ Schatz M Nagarajan N Acob RA Guan P Blas A Wai CM Ackerman CM Ren Y Liu C Wang J Wang J Na JK Shakirov EV Haas B Thimmapuram J Nelson D Wang X Bowers JE Gschwend AR Delcher AL Singh R Suzuki JY Tripathi S Neupane K Wei H Irikura B Paidi M Jiang N Zhang W 《Nature》2008,452(7190):991-996
Papaya, a fruit crop cultivated in tropical and subtropical regions, is known for its nutritional benefits and medicinal applications. Here we report a 3x draft genome sequence of 'SunUp' papaya, the first commercial virus-resistant transgenic fruit tree to be sequenced. The papaya genome is three times the size of the Arabidopsis genome, but contains fewer genes, including significantly fewer disease-resistance gene analogues. Comparison of the five sequenced genomes suggests a minimal angiosperm gene set of 13,311. A lack of recent genome duplication, atypical of other angiosperm genomes sequenced so far, may account for the smaller papaya gene number in most functional groups. Nonetheless, striking amplifications in gene number within particular functional groups suggest roles in the evolution of tree-like habit, deposition and remobilization of starch reserves, attraction of seed dispersal agents, and adaptation to tropical daylengths. Transgenesis at three locations is closely associated with chloroplast insertions into the nuclear genome, and with topoisomerase I recognition sites. Papaya offers numerous advantages as a system for fruit-tree functional genomics, and this draft genome sequence provides the foundation for revealing the basis of Carica's distinguishing morpho-physiological, medicinal and nutritional properties. 相似文献