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81.
Low gene copy number shows that arbuscular mycorrhizal fungi inherit genetically different nuclei 总被引:1,自引:0,他引:1
Arbuscular mycorrhizal fungi (AMF) are ancient asexually reproducing organisms that form symbioses with the majority of plant species, improving plant nutrition and promoting plant diversity. Little is known about the evolution or organization of the genomes of any eukaryotic symbiont or ancient asexual organism. Direct evidence shows that one AMF species is heterokaryotic; that is, containing populations of genetically different nuclei. It has been suggested, however, that the genetic variation passed from generation to generation in AMF is simply due to multiple chromosome sets (that is, high ploidy). Here we show that previously documented genetic variation in Pol-like sequences, which are passed from generation to generation, cannot be due to either high ploidy or repeated gene duplications. Our results provide the clearest evidence so far for substantial genetic differences among nuclei in AMF. We also show that even AMF with a very large nuclear DNA content are haploid. An underlying principle of evolutionary theory is that an individual passes on one or half of its genome to each of its progeny. The coexistence of a population of many genomes in AMF and their transfer to subsequent generations, therefore, has far-reaching consequences for understanding genome evolution. 相似文献
82.
Functional profiling of the Saccharomyces cerevisiae genome 总被引:1,自引:0,他引:1
Giaever G Chu AM Ni L Connelly C Riles L Véronneau S Dow S Lucau-Danila A Anderson K André B Arkin AP Astromoff A El-Bakkoury M Bangham R Benito R Brachat S Campanaro S Curtiss M Davis K Deutschbauer A Entian KD Flaherty P Foury F Garfinkel DJ Gerstein M Gotte D Güldener U Hegemann JH Hempel S Herman Z Jaramillo DF Kelly DE Kelly SL Kötter P LaBonte D Lamb DC Lan N Liang H Liao H Liu L Luo C Lussier M Mao R Menard P Ooi SL Revuelta JL Roberts CJ Rose M Ross-Macdonald P Scherens B Schimmack G 《Nature》2002,418(6896):387-391
Determining the effect of gene deletion is a fundamental approach to understanding gene function. Conventional genetic screens exhibit biases, and genes contributing to a phenotype are often missed. We systematically constructed a nearly complete collection of gene-deletion mutants (96% of annotated open reading frames, or ORFs) of the yeast Saccharomyces cerevisiae. DNA sequences dubbed 'molecular bar codes' uniquely identify each strain, enabling their growth to be analysed in parallel and the fitness contribution of each gene to be quantitatively assessed by hybridization to high-density oligonucleotide arrays. We show that previously known and new genes are necessary for optimal growth under six well-studied conditions: high salt, sorbitol, galactose, pH 8, minimal medium and nystatin treatment. Less than 7% of genes that exhibit a significant increase in messenger RNA expression are also required for optimal growth in four of the tested conditions. Our results validate the yeast gene-deletion collection as a valuable resource for functional genomics. 相似文献
83.
Mohamed?A.?Wahdan Pieter?Spronck Hamdi?F.?Ali Eddy?Vaassen H.?Jaap?Van Den?HerikEmail author 《Systemic Practice and Action Research》2005,18(6):569-580
Most corporations are required by law to produce annual reports on their financial positions. These financial reports are accompanied by an auditor's report, which is an independent auditor's opinion on the fairness of the financial statements. To formulate their reports, auditors use a “personal-judgement” approach that heavily depends on their experience and expertise. This approach may be (1) ineffective and may lead to (2) different decisions, (3) personal bias, and (4) misleading judgements. These four drawbacks of a human auditor are a source of doubt and hesitation for every corporation. Therefore, the challenging question is: Can a computer do a better job? This paper focuses on the construction and implementation of a knowledge-based system, called the “Auditor's Report EXpert” (AREX), that is capable of formulating the opinion on financial statements, as expressed in the auditor's report. The knowledge used by AREX is acquired from the literature, and from a slate of practicing and academic auditors by means of questionnaires and in-depth interviews. A preliminary validation of AREX indicates that AREX is successful in performing the auditor's report task. Hence, we tentatively conclude that currently a computer program can support an auditor in his/her task. Moreover, in the foreseeable futur's reports that are effective, universal in their decisions, do not show a personal bias, and do not have misleading statements. 相似文献
84.
Effectiveness of the global protected area network in representing species diversity 总被引:7,自引:0,他引:7
Rodrigues AS Andelman SJ Bakarr MI Boitani L Brooks TM Cowling RM Fishpool LD Da Fonseca GA Gaston KJ Hoffmann M Long JS Marquet PA Pilgrim JD Pressey RL Schipper J Sechrest W Stuart SN Underhill LG Waller RW Watts ME Yan X 《Nature》2004,428(6983):640-643
The Fifth World Parks Congress in Durban, South Africa, announced in September 2003 that the global network of protected areas now covers 11.5% of the planet's land surface. This surpasses the 10% target proposed a decade earlier, at the Caracas Congress, for 9 out of 14 major terrestrial biomes. Such uniform targets based on percentage of area have become deeply embedded into national and international conservation planning. Although politically expedient, the scientific basis and conservation value of these targets have been questioned. In practice, however, little is known of how to set appropriate targets, or of the extent to which the current global protected area network fulfils its goal of protecting biodiversity. Here, we combine five global data sets on the distribution of species and protected areas to provide the first global gap analysis assessing the effectiveness of protected areas in representing species diversity. We show that the global network is far from complete, and demonstrate the inadequacy of uniform--that is, 'one size fits all'--conservation targets. 相似文献
85.
Summary Invertase activity has been studied in the fore-, mid- and hindgut of the 6th instar larva ofSpodoptera mauritia. The highest activity was in the midgut except during the early hours of the larval period when the foregut showed comparatively increased activity. The hindgut invertase activity may be from the voiding of enzyme along with the undigested food.Acknowledgments. The authors wish to thank the Department of Zoology, for providing the facilities for this work. The senior author gratefully acknowledges the junior research fellowship from the University of Calicut. 相似文献
86.
Subarya C Chlieh M Prawirodirdjo L Avouac JP Bock Y Sieh K Meltzner AJ Natawidjaja DH McCaffrey R 《Nature》2006,440(7080):46-51
The Sumatra-Andaman earthquake of 26 December 2004 is the first giant earthquake (moment magnitude M(w) > 9.0) to have occurred since the advent of modern space-based geodesy and broadband seismology. It therefore provides an unprecedented opportunity to investigate the characteristics of one of these enormous and rare events. Here we report estimates of the ground displacement associated with this event, using near-field Global Positioning System (GPS) surveys in northwestern Sumatra combined with in situ and remote observations of the vertical motion of coral reefs. These data show that the earthquake was generated by rupture of the Sunda subduction megathrust over a distance of >1,500 kilometres and a width of <150 kilometres. Megathrust slip exceeded 20 metres offshore northern Sumatra, mostly at depths shallower than 30 kilometres. Comparison of the geodetically and seismically inferred slip distribution indicates that approximately 30 per cent additional fault slip accrued in the 1.5 months following the 500-second-long seismic rupture. Both seismic and aseismic slip before our re-occupation of GPS sites occurred on the shallow portion of the megathrust, where the large Aceh tsunami originated. Slip tapers off abruptly along strike beneath Simeulue Island at the southeastern edge of the rupture, where the earthquake nucleated and where an M(w) = 7.2 earthquake occurred in late 2002. This edge also abuts the northern limit of slip in the 28 March 2005 M(w) = 8.7 Nias-Simeulue earthquake. 相似文献