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961.
During meiosis, crossing-over--the exchange of genetic material between maternal and paternal chromosomes--is stringently controlled to restrict the number of crossovers per chromosome pair. In this issue of Cell, Martini et al., (2006) report that the reduction of crossover-initiating events does not result in fewer crossovers. These results have important implications for our understanding of crossover control. 相似文献
962.
利用AFLP遗传连锁图定位大麦苗期对叶锈病的部分抗性基因 总被引:11,自引:0,他引:11
借助大麦染色体AFLP标记遗传连锁图和MapQTLV3.0作图软件,对大麦叶病的数量抗性基因进行了定位分析,明确了大麦部分抗性品种Vada对叶锈病的潜育期由分别位于染色体1、2、6、7上离短臂末端79cM、186cM、58cM和117cM处的4个数量抗性基因所控制。 相似文献
963.
Ákos Szekrényes SungAe Suhr Park Marcia Santos Clarence Lew Aled Jones Ted Haxo 《MABS-AUSTIN》2016,8(1):56-64
An international team that included 20 independent laboratories from biopharmaceutical companies, universities, analytical contract laboratories and national authorities in the United States, Europe and Asia was formed to evaluate the reproducibility of sample preparation and analysis of N-glycans using capillary electrophoresis of 8-aminopyrene-1,3,6-trisulfonic acid (APTS)-labeled glycans with laser induced fluorescence (CE-LIF) detection (16 sites) and ultra high-performance liquid chromatography (UHPLC, 12 sites; results to be reported in a subsequent publication). All participants used the same lot of chemicals, samples, reagents, and columns/capillaries to run their assays. Migration time, peak area and peak area percent values were determined for all peaks with >0.1% peak area. Our results demonstrated low variability and high reproducibility, both, within any given site as well across all sites, which indicates that a standard N-glycan analysis platform appropriate for general use (clone selection, process development, lot release, etc.) within the industry can be established. 相似文献
964.
The transfer of label from 15N-alanine and 15N-glutamate into amino acids in incubated brain slices has been followed using gas chromatography/mass spectrometry (GC/MS). 15N from alanine appeared in both amino and amide groups of glutamine more rapidly than into aspartate, glutamate and GABA, which were all labeled at similar rates. Maximum labelling of approx. 50% enrichment of these three metabolites was achieved in 3 hr. The 15N present in doubly-labeled glutamine exceeded that in the singly-labelled after 30 min. 15N from glutamate was rapidly transferred to aspartate and to alanine, with slower incorporation into glutamine and GABA. As was seen with labeling from alanine, doubly-labeled glutamine was higher than the singly-labeled species, also reaching some 50% enrichment in 3 hr. Depolarisation with 40 mM extracellular K+ caused a considerable reversal of the ratio of doubly- to singly-labeled glutamine species from both alanine and glutamate. The results are discussed in terms of the effects of depolarization on the glutamate/glutamine cycle. 相似文献
965.
Isoprene emission from plants is one of the principal ways in which plant processes alter atmospheric chemistry. Despite
the importance of this process, few long-term controls over basal emission rates have been identified. Stress-induced changes
in carbon allocation within the entire plant, such as those produced by defoliation, have not been examined as potential mechanisms
that may control isoprene production and emission. Eastern cottonwood (Populus deltoides) saplings were partially defoliated and physiological and growth responses were measured from undamaged and damaged leaves
7 days following damage. Defoliation reduced isoprene emission from undamaged and damaged leaves on partially defoliated plants.
Photosynthetic rates and leaf carbon and nitrogen pools were unaffected by damage. Photosynthetic rate and isoprene emission
were highly correlated in undamaged leaves on undamaged plants and damaged leaves on partially defoliated plants. There was
no correlation between photosynthetic rate and isoprene emission in undamaged leaves on partially defoliated plants. Isoprene
emission was also highly correlated with the number of source leaves on the apical shoot in damage treatments. Increased carbon
export from source leaves in response to defoliation may have depleted the amount of carbon available for isoprene synthesis,
decreasing isoprene emission. These results suggest that while isoprene emission is controlled at the leaf level in undamaged
plants, emission from leaves on damaged plants is controlled by whole-branch allocation patterns.
Received: 12 May 1998 / Accepted: 9 November 1998 相似文献
966.
Andrew Gall Justin P. Ridge Bruno Robert Richard J. Cogdell Michael R. Jones Paul K. Fyfe 《Photosynthesis research》1999,59(2-3):223-230
The effect of mutagenesis on the detailed conformation of the carotenoid cofactor of the bacterial reaction centre has been examined using resonance Raman spectroscopy. Four single site mutations were made, removing polar residues that line the binding pocket for spheroidenone in the reaction centre from Rhodobacter sphaeroides. All of the mutations caused changes in the relative intensity of bands in the 2 frequency region of the carotenoid resonance Raman spectrum, suggesting a change in the geometry of the central 15,15-cis bond of the spheroidenone. In addition, increased splitting of the 1 vibrational modes in two of the mutant RCs indicated a reduction of the effective conjugation length of the spheroidenone, possibly due to an increased distortion from a planar geometry along the C=C backbone of the spheroidenone. These changes in the detailed conformation of the reaction centre carotenoid do not affect the optical properties o f the cofactor, and are beyond the limits of detection of X-ray crystallography as currently applied to the bacterial reaction centre. 相似文献
967.
Recent studies demonstrate positive density-dependent feedbacks between animal populations and their resource supply that result in increased individual fitness at high densities. Such feedbacks occur in both terrestrial and aquatic organisms not showing strong social organization. A number of different mechanisms are involved. Detecting positive feedbacks in natural populations may not be possible from simple correlations between resource abundance and animal population density in space or time, but experimental manipulation of resource supply or animal density can reveal their presence. Positive feedbacks may result in higher equilibrium densities of animal populations, alter the density range over which intraspecific competition is detectable, and offer a resource-based explanation for the evolution of gregariousness and social organization. 相似文献
968.
Neely RK Daujotyte D Grazulis S Magennis SW Dryden DT Klimasauskas S Jones AC 《Nucleic acids research》2005,33(22):6953-6960
DNA base flipping is an important mechanism in molecular enzymology, but its study is limited by the lack of an accessible and reliable diagnostic technique. A series of crystalline complexes of a DNA methyltransferase, M.HhaI, and its cognate DNA, in which a fluorescent nucleobase analogue, 2-aminopurine (AP), occupies defined positions with respect the target flipped base, have been prepared and their structures determined at higher than 2 Å resolution. From time-resolved fluorescence measurements of these single crystals, we have established that the fluorescence decay function of AP shows a pronounced, characteristic response to base flipping: the loss of the very short (~100 ps) decay component and the large increase in the amplitude of the long (~10 ns) component. When AP is positioned at sites other than the target site, this response is not seen. Most significantly, we have shown that the same clear response is apparent when M.HhaI complexes with DNA in solution, giving an unambiguous signal of base flipping. Analysis of the AP fluorescence decay function reveals conformational heterogeneity in the DNA–enzyme complexes that cannot be discerned from the present X-ray structures. 相似文献
969.
Jason Jones Christine E. Gibb Susanne C. Millard Jennifer J. Barg† M. Katharine Girvan‡ M. Lisa Veit§ Vicki L. Friesen Raleigh J. Robertson 《Journal of Biogeography》2005,32(10):1827-1833
Aim Bergmann's rule, the tendency for body size to be positively correlated with latitude, is widely accepted but the mechanisms behind the patterns are still debated. Bergmann's originally conceived mechanism was based on heat conservation; other proposed mechanisms invoke phylogeny, migration distance and resource seasonality. With the goal of examining these mechanisms, we quantified morphological variation across the breeding range of a Neotropical migratory songbird, the cerulean warbler (Dendroica cerulea). Location Deciduous forests of eastern North America. Methods We sampled nine cerulean warbler populations, spanning the species’ breeding range. We captured 156 males using targeted playback and model presentation, and included 127 adult males in our analyses of morphological variation. We used an information‐theoretical approach to identify climatic variables associated with geographical variation in body size. Results Cerulean warbler body size adheres to Bergmann's rule: individuals in northern populations are larger than those in southern populations. Variation in body size is best explained by variation in dry and wet‐bulb temperature and actual evapotranspiration. Main conclusions Adherence to Bergmann's rule by the cerulean warbler appears to be linked to thermodynamics (heat conservation in the north, evaporative cooling in the south) and resource seasonality. Multiple selection pressures can interact to generate a single axis of morphological geographical variation, and even subtle fluctuations in climatic variables can exert significant selection pressures. We suggest that the influence of selection pressures on migrants might be enhanced by migratory connectivity, providing further support for the important role played by this phenomenon in the ecology, evolution and population dynamics of migratory songbirds. 相似文献
970.
C Gessert J Blossom P Sommers M D Canfield C Jones 《The Western journal of medicine》1989,150(2):226-230
Graduates of four rural and four urban family practice programs were interviewed to determine the nature of their practices and the factors that had influenced their practice location decisions. All programs gave residents substantial experience providing continuity of care for underserved populations. Of the 158 physicians surveyed, 58 (46%) were working in areas designated as underserved. The percentage of physicians in underserved areas was higher than that reported in other studies and was much higher than would be expected if practice sites were selected on the basis of population distribution alone. Notable differences in personal and practice characteristics were found between the physicians who chose to work in underserved areas and those who did not and between those who established practices in rural and in urban underserved areas. 相似文献