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Carrots, celery, caraway and cumin and their relatives in the Apiaceae (Umbelliferae) have a long history of human use dating from our earliest written records. A large body of folklore has accumulated on their magical and mythical curative properties. Many of the early uses have persisted as part of 20th century folklore, sometimes supplementary to modern medicine. Studies largely during the last half of this century have provided the chemical bases for some of the ancient cures.  相似文献   

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A series of important new theoretical, experimental and observational studies demonstrate that just a few immigrants can have positive immediate impacts on the evolutionary trajectory of local populations. In many cases, a low level of immigration into small populations has produced fitness benefits that are greater than those predicted by theoretical models, resulting in what has been termed 'genetic rescue'. However, the opposite result (reduced fitness) can also be associated with immigration of genetically divergent individuals. Central to our understanding of genetic rescue are complex interactions among fundamental concepts in evolutionary and population biology, including both genetic and non-genetic (environmental, behavioral and demographic) factors. Developing testable models to predict when genetic rescue is likely to occur is a daunting challenge that will require carefully controlled, multi-generation experiments as well as creative use of information from natural 'experiments'.  相似文献   

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Most researchers confidently assume that transformation of recombinant plasmid libraries into microbial hosts followed by outgrowth of isolated colonies results in a "one cell-one mutant gene-one protein variant" paradigm. Indeed, this assumption is supported by the overwhelming majority of published studies employing bacterial expression hosts. In stark contrast, we recently reported on Saccharomyces cerevisiae libraries containing unexpectedly high frequencies of cells harboring heterogeneous mixtures of plasmids, so called Multiple Vector Transformants (MVT). Intriguingly, we observed that yeast MVT persist as a significant proportion of populations for multiple generations. MVT can lead to misidentification of isolated mutants loss of functionally enhanced clones, and unwitting propagation of false positives derived from contaminating control sequences. Such experimental complications can have devastating outcomes in the context of protein engineering by combinatorial library screening. Herein, we demonstrate that the phenomenon of MVT is not restricted to vectors bearing the CEN/ARSH origin of replication, but may be an even greater concern when using high copy 2 μm plasmids. To mitigate the risks associated with MVT, we have developed an optimized sequencing procedure that facilitates rapid and reliable identification of MVT among clones of interest. In our experience, MVT and their associated risks can be virtually eliminated by employing extended liquid outgrowths of transformed populations and archiving sequence-verified, monoclonal, mutant genes from cell-templated PCR amplicons.  相似文献   

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It has long been accepted that the pattern of occurrence of scrapie--the form of spongiform encephalopathy associated with sheep--is determined mainly by maternal transmission, and this view has had a profound influence on policy decisions in the control of bovine spongiform encephalopathy and on public concern over the risk to human health form this disease. The occurrence of maternal transmission is, however, not predicted by modern knowledge of the aetiology of spongiform encephalopathy, and even though claims of maternal transmission have been reiterated frequently in the literature, re-examination of the source data reveals that these data are extremely scanty, unreplicated, and probably subject to ascertainment bias. The probability of maternal transmission of spongiform encephalopathy in any species should be viewed with the greatest scepticism.  相似文献   

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Technology development is innovative to many aspects of basic and applied plant transgenic science. Plant genetic engineering has opened new avenues to modify crops, and provided new solutions to solve specific needs. Development of procedures in cell biology to regenerate plants from single cells or organized tissue, and the discovery of novel techniques to transfer genes to plant cells provided the prerequisite for the practical use of genetic engineering in crop modification and improvement. Plant transformation technology has become an adaptable platform for cultivar improvement as well as for studying gene function in plants. This success represents the climax of years of efforts in tissue culture improvement, in transformation techniques and in genetic engineering. Plant transformation vectors and methodologies have been improved to increase the efficiency of transformation and to achieve stable expression of transgenes in plants. This review provides a comprehensive discussion of important issues related to plant transformation as well as advances made in transformation techniques during three decades.  相似文献   

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C Richmond 《CMAJ》1996,154(3):378-381
Health care: public, private or both? In Great Britain, about 13% of the population is covered by private health insurance, and everyone else is served by the public health care system known as the National Health Service, or NHS. Caroline Richmond, who examined the impact of private medical practice in Britain, says people become private patients for one compelling reason: to avoid the NHS''s notoriously long waiting lists for surgery. According to Professor Alan Maynard, a health care researcher, the mainstays of the private sector are the "three h''s" --hips, hernias and hemorrhoids-- along with some elective surgery, particularly in gynecology and opthalmology. Another small sector focuses on fertility regulation and cosmetic surgery. Although the levels are not monitored closely, physician consultants are not permitted to earn more than 10% of their income from private practice.  相似文献   

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The existence of a medicinal 'biotech revolution' has been widely accepted and promoted by academics, consultants, industry and government. This has generated expectations about significant improvements in the drug discovery process, healthcare and economic development that influence a considerable amount of policy-making. Here we present empirical evidence, from a variety of indicators, that shows that a range of outputs have failed to keep pace with increased research and development spending. Rather than producing revolutionary changes, medicinal biotechnology is following a well-established pattern of slow and incremental technology diffusion. Consequently, many expectations are wildly optimistic and over-estimate the speed and extent of the impact of biotechnology, suggesting that the assumptions underpinning much contemporary policymaking need to be rethought.  相似文献   

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Plant species assemblages, communities or regional floras might be termed 'saturated' when additional immigrant species are unsuccessful at establishing due to competitive exclusion or other inter-specific interactions, or when the immigration of species is off-set by extirpation of species. This is clearly not the case for state, regional or national floras in the USA where colonization (i.e. invasion by exotic species) exceeds extirpation by roughly a 24 to 1 margin. We report an alarming temporal trend in plant invasions in the Pacific Northwest over the past 100 years whereby counties highest in native species richness appear increasingly invaded over time. Despite the possibility of some increased awareness and reporting of native and exotic plant species in recent decades, historical records show a significant, consistent long-term increase in exotic species (number and frequency) at county, state and regional scales in the Pacific Northwest. Here, as in other regions of the country, colonization rates by exotic species are high and extirpation rates are negligible. The rates of species accumulation in space in multi-scale vegetation plots may provide some clues to the mechanisms of the invasion process from local to national scales.  相似文献   

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