共查询到14条相似文献,搜索用时 0 毫秒
1.
Neutral dynamics occur in evolution if all types are ‘effectively equal’ in their reproductive success, where the definition of ‘effectively equal’ depends on the population size and the details of mutations. Empirically observed neutral genetic evolution in extremely large clonal populations can only be explained under current models if selection is completely absent. Such models typically consider the case where population dynamics occurs on a different timescale to evolution. However, this assumption is invalid when mutations are not rare in a whole population. We show that this has important consequences for the occurrence of neutral evolution in clonal populations. In highly connected type spaces, neutral dynamics can occur for all population sizes despite significant selective differences, via the forming of effectively neutral networks connecting rare neutral types. Biological implications include an explanation for the high diversity of rare types that survive in large clonal populations, and a theoretical justification for the use of neutral null models. 相似文献
2.
Bilateral similarity function is designed for analyzing the similarities of biological sequences such as DNA, RNA secondary structure or protein in this paper. The defined function can perform comprehensive comparison between sequences remarkably well, both in terms of the Hamming distance of two compared sequences and the corresponding location difference. Compared with the existing methods for similarity analysis, the examination of similarities/dissimilarities illustrates that the proposed method with the computational complexity of O(N) is effective for these three kinds of biological sequences, and bears the universality for them. 相似文献
3.
Background
Complete analysis of single substrate enzyme-catalyzed reactions has required a separate use of two distinct approaches. Steady state approximations are employed to obtain substrate affinity and initial velocity information. Alternatively, first order exponential decay models permit simulation of the time course data for the reactions. Attempts to use integrals of steady state equations to describe reaction time courses have so far met with little success.Methods
Here we use equations based on steady state approximations to directly model time course plots.Results
Testing these expressions with the enzyme β-galactosidase, which adheres to classical Michaelis–Menten kinetics, produced a good fit between observed and calculated values.General significance
This study indicates that, in addition to providing information on initial kinetic parameters, steady state approximations can be employed to directly model time course kinetics.Integrated forms of the Michaelis–Menten equation have previously been reported in the literature. Here we describe a method to directly apply steady state approximations to time course analysis for predicting product formation and simultaneously obtain multiple kinetic parameters. 相似文献4.
Yuji Kishi 《Population Ecology》1979,20(2):211-215
The graphical technique devised bySmith andFretwell (1974) to construct a model of the optimal offspring size was applied to the case where disruptive selection might work on offspring size. On this basis, a possible case of speciation in freshwater gobies characterized by egg-size difference was discussed. 相似文献
5.
We examine properties of adaptive walks on uncorrelated (i.e. random) fitness landscapes starting from moderately fit genotypes under strong selection weak mutation. As an extension of Orr's model for a single step in an adaptive walk under these conditions, we show that the fitness rank of the dominant genotype in a population after the fixation of a beneficial mutation is, on average, (i+6)/4, where i is the fitness rank of the starting genotype. This accounts for the change in rank due to acquiring a new set of single-mutation neighbors after fixing a new allele through natural selection. Under this scenario, adaptive walks can be modeled as a simple Markov chain on the space of possible fitness ranks with an absorbing state at i = 1, from which no beneficial mutations are accessible. We find that these walks are typically short and are often completed in a single step when starting from a moderately fit genotype. As in Orr's original model, these results are insensitive to both the distribution of fitness effects and most biological details of the system under consideration. 相似文献
6.
7.
8.
We present an initial attempt for the development of a distributed and scalable GIS-like tool for the storage, selection and visualization of 4D marine datasets. The aim of this tool is to standardize the variety of data available for the water column and support non-technical marine biologists in manipulating 4D marine datasets. The tool is developed towards answering specific environmental and biological questions regarding ocean processes and essential fish habitat mapping in three dimensions. Guest editor: V. D. Valavanis Essential Fish Habitat Mapping in the Mediterranean 相似文献
9.
Jordan D. R. Tao Y. Z. Godwin I. D. Henzell R. G. Cooper M. McIntyre C. L. 《Molecular breeding : new strategies in plant improvement》2005,14(4):441-454
Seventy sorghum inbred lines which formed part of the Queensland Department of Primary Industries (QDPI) sorghum breeding program were screened with 104 previously mapped RFLP markers. The lines were related by pedigree and consisted of ancestral source lines, intermediate lines and recent releases from the program. We compared the effect of defining marker alleles using either identity by state (IBS) or identity by descent (IBD) on our capacity to trace markers through the pedigree and detect evidence of selection for particular alleles. Allelic identities defined using IBD were much more sensitive for detecting non-Mendelian segregation in this pedigree. Only one marker allele showed significant evidence of selection when IBS was used compared with ten regions with particular allelic identities when IBD was used. Regions under selection were compared with the location of QTLs for agronomic traits known to be under selection in the breeding program. Only two of the ten regions were associated with known QTLs that matched with knowledge of the agronomic characteristics of the ancestral lines. Some of the other regions were hypothesised to be associated with genes for particular traits based on the properties of the ancestral source lines. 相似文献
10.
The liver mitochondrial and microsomal membranes of green sunfish and rat were examined by steady state polarisation and differential polarised phase fluorimetry to determine the effects of seasonal adaptation of membrane dynamic structure to temperature. Steady state polarisation studies indicated that the liver mitochondria of green sunfish acclimated to different temperatures showed a greater partial compensation of membrane fluidity for the altered acclimation temperature than did liver microsomal membranes. The fatty acid composition of both membrane preparations generally became more unsaturated at lower acclimation temperatures, though the differences between 5°C and 25°C acclimated fish were more pronounced in the mitochondrial fraction than in the microsomal fraction.Differential polarised phase fluorimetric studies indicated that the rotations of diphenylhexatriene in mitochondrial and microsomal membranes were highly hindered, though the hindrance offered by membranes of 25°C acclimated green sunfish was far greater than that offered by the membranes of 5°C acclimated fish, thus supporting the concept of homeoviscous adaptation. The absolute rotational rate was not consistently affected by acclimation treatment. 相似文献
11.
Iron release from human serum transferrin (hTF) has been studied extensively; however, the molecular details of the mechanism(s)
remain incomplete. This is in part due to the complexity of this process, which is influenced by lobe–lobe interactions, the
transferrin receptor (TFR), the salt effect, the presence of a chelator, and acidification within the endosome, resulting
in iron release. The present work brings together many of the concepts and assertions derived from previous studies in a methodical,
uniform, and visual manner. Examination of earlier work reveals some uncertainty due to sample and technical limitations.
We have used a combination of steady-state fluorescence and urea gels to evaluate the effect of conformation, pH, time, and
the soluble portion of the TFR (sTFR) on iron release from each lobe of hTF. The use of authentic recombinant monoferric and
locked species removes any possibility of cross-contamination by acquisition of iron. Elimination of detergent by use of the
sTFR provides a further technical advantage. We find that iron release from the N-lobe is very sensitive to the conformation
of the C-lobe, but is insensitive to the presence of the sTFR or to changes in pH (between 5.6 and 6.4). Specifically, when
the cleft of the C-lobe is locked, the urea gels indicate that only about half of the iron is completely removed from the
cleft of the N-lobe. Iron release from the C-lobe is most affected by the presence of the sTFR and changes in pH, but is unaffected
by the conformation of the N-lobe. A model for iron release from diferric hTF is provided to delineate our findings.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
12.
Quince (Cydonia oblonga Mill.), pear (Pyrus communis L.) and olive (Olea europaea L.) genotypes were evaluated for their tolerance to iron deficiency stress by growing young plants in three types of aerated nutrient solutions: (1) with iron, (2) without iron or (3) low in iron and with 10 mM bicarbonate. Plants were obtained either from rooted softwood cuttings or from germination of seeds. The degree of tolerance was evaluated with several indices: (1) the chlorophyll content, (2) the root Fe3+ reducing capacity and (3) the whole plant relative growth. Fifteen hours before Fe3+ reducing capacity determination, iron was applied to the roots of plants with iron-stress, since this method resulted in increasing the reductase activity. All quince and pear genotypes increased the root Fe3+ reducing capacity when grown in the treatments for iron-stress, in relation to control plants of the same genotypes. In olive cultivars, the Fe3+ reducing capacity was lower in the iron-stress treatments than in the control one. Studying the relationship between relative growth and chlorophyll content for each genotype under iron-stress, in relation to both indices in control plants, a classification of species and genotypes was established. According to that, most olive cultivars and some pear rootstocks and cultivars appear more iron-efficient than quince rootstocks. Our study shows that in some woody species, determining root Fe3+ reducing capacity is not the best method to establish tolerance to iron deficiency stress. 相似文献
13.
Quantifying the habitat structure and spatial pattern of New Jersey (U.S.A.) salt marshes under different management regimes 总被引:3,自引:0,他引:3
Mosquito control measures have resulted in majorstructural alterations of many coastal marshes, withrelatively unknown consequences to larger ecosystemfunctioning. Parallel grid ditching and open marshwater management (OMWM) techniques are purposefullydesigned to alter the hydrological regime and therelative availability and/or characteristics ofstanding water on the marsh surface. With the growingrecognition of the important influence that habitatstructure and the configuration of the marsh-edgeboundary has on nekton utilization of salt marshsystems, the impact of mosquito control managementtechniques on the availability and quality of saltmarsh habitat deserves increased scrutiny. Usingdigital image processing techniques, we completed adetailed mapping effort for a 1800 ha study area inTuckerton, New Jersey to provide a picture ofsubtidal and intertidal habitat availability. Spatialanalysis techniques were used to quantify the relativeamount of habitat types and spatial pattern of theland-water interface under different managementregimes: parallel grid-ditched, OMWM and an unalteredreference. The parallel grid-ditched site had a muchlower incidence of marsh ponds which serve asimportant low tide and over-wintering refuge forcertain species of fish. In comparison, the OMWM sitehad a much greater amount of ponded water habitats.The grid-ditched site had a higher density of marshsurface-to-tidal water interface resulting in a lowermedian distance between the marsh interior and theadjacent tidal channel network. This study serves tobenchmark the habitat structure and spatial pattern ofa highly functioning natural marsh for use as areference site in regional wetland creation orrestoration efforts. 相似文献
14.
C. A. MCALPINE J. SYKTUS† J. G. RYAN R. C. DEO G. M. MCKEON† H. A. MCGOWAN S. R. PHINN 《Global Change Biology》2009,15(9):2206-2223
Global climate change is the major and most urgent global environmental issue. Australia is already experiencing climate change as evidenced by higher temperatures and more frequent and severe droughts. These impacts are compounded by increasing land use pressures on natural resources and native ecosystems. This paper provides a synthesis of the interactions, feedbacks and risks of natural climate variability, climate change and land use/land cover change (LUCC) impacting on the Australian continent and how they vary regionally. We review evidence of climate change and underlying processes resulting from interactions between global warming caused by increased concentration of atmospheric greenhouse gases and modification of the land surface. The consequences of ignoring the effect of LUCC on current and future droughts in Australia could have catastrophic consequences for the nation's environment, economy and communities. We highlight the need for more integrated, long-term and adaptive policies and regional natural resource management strategies that restore the beneficial feedbacks between native vegetation cover and local-regional climate, to help ameliorate the impact of global warming. 相似文献