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111.
To obtain an insight into the evolutionary origin of the major histocompatibility complex (MHC) class I polymorphism, a cDNA library was prepared from a heterozygous chimpanzee cell line expressing MHC class I molecules crossreacting with allele-specific HLA-A11 antibodies. The library was screened with human class I locus-specific DNA probes, and clones encoding both alleles at the A and B loci have been identified and sequenced. In addition, the sequences of two HLA-A11 subtypes differing by a single nucleotide substitution have been obtained. The comparison of chimpanzee and human sequences revealed a close similarity (up to 98.5%). The chimpanzee A locus alleles showed greatest similarity to the human HLA-A11/A3 family of alleles, one of them being very close to HLA-A11. Similarly, segments of the ChLA-B alleles displayed greatest similarity to certain HLA-B alleles. The calculated evolutionary branch point for the A11-like alleles is 7 x 10(6) to 9 x 10(6) years, whereas the other A locus alleles diverged between 12 x 10(6) and 17 x 10(6) years ago. Since the human and chimpanzee lineages separated 5 x 10(6) to 7 x 10(6) years ago, our data support the notion that during evolution, MHC alleles are transmitted from one species to the next.  相似文献   
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113.
Eine Tendenz findet ihren Ausdruck, im Laufe der Evolution im Pflanzenreich, in gleichartigen Phänomenen, welche aber unabhängig voneinander und bisweilen in verschiedener Weise auftreten, in verschiedenen und nicht notwendig nah verwandten Pflanzengruppen, und außerdem in ganz verschiedenen geologischen Perioden. Einige Beispiele werden gegeben: die Tendenz zur Differenzierung in Stamm, Blätter und Wurzel; die Tendenz zur Heterosporie; die Tendenz zur Angiospermie. Der Tendenzbegriff ist nicht identisch mit Konvergenz oder Parallelismus; er ist nicht die Folge von ökologisch-gleichartigen Lebensverhältnissen (Anpassungsähnlichkeiten), und meistens handelt es sich auch nicht um Gestaltsähnlichkeiten der Totalität des Organismus. Tendenzen beschränken sich meistens auf einzelne Organe. Gegründet auf den Tendenzbegriff wird die Evolution der Landpflanzen zu den Angiospermen beleuchtet, ausgehend von isosporen Pteridophyten. Die in Betracht gezogenen Tendenzen sind nacheinander: 1. die Tendenz zur Heterosporie; 2. die Tendenz einer Reduktion der Zahl der Makrosporen im Makrosporangium bis einer einzigen Makrospore; 3. die Tendenzen zu dem Entstehen von Präovula und Präpollen; 4. die Tendenzen zur Bildung von Samenanlagen und Pollen; 5. die Tendenz zur Angiovulie und Angiospermie. Diese Tendenzen zeigen uns wichtige Evolutionsschritte als zwar gleichartige, aber oft recht verschiedene und unabhängig auftretende Phänomene.  相似文献   
114.
Density‐dependent reproduction is commonly explained by either the habitat heterogeneity (HHH) or individual adjustment (IAH) hypothesis. Under the HHH, high quality territories are assumed to be occupied first. At higher density, occupation of low‐quality territories increases due to lower availability of high‐quality territories, which reduces mean reproductive success. Alternatively, the IAH assumes that increased competition at higher densities reduces reproductive success in all territories. For birds of prey, HHH plays an important role in territorial species, and IAH in socially breeding species. To test the generality of this hypothesis, we studied the mechanism behind density dependence in raven Corvus corax, a long‐lived passerine bird, using long‐term population data from a large number of territories. Population density decreased reproduction, which was explained by increased usage of low quality territories at higher density, supporting the HHH. Density reduced reproduction in low quality territories, but not in high and intermediate quality territories. We additionally compared the explanatory power of different models describing brood size, representing IAH, HHH, or a combination of both. The best model represented a combination of both hypotheses, in which the effect of density depended on territory quality. Our conclusion that both IAH and HHH are supported can be explained by the biology of ravens, where territorial adults not only experience interference competition with other territorial adults, but also with social groups of juveniles and floaters. We conclude that the relative importance of IAH and HHH may depend on variation in territory quality and social structure.  相似文献   
115.
Relaxation dynamics is universal in science and engineering; its study serves to parameterize a system's response and to help identify a microscopic model of the processes involved. When measured data for a phenomenon cannot be fitted using one exponential, the choice of an alternative function to describe the decay becomes nontrivial. Here, we contrast two different, but fundamentally related approaches to fitting nontrivial decay curves; exponential decomposition and the gamma probability density function. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
116.
For many diseases, it seems that the age at onset is geneticallyinfluenced. Therefore, the age-at-onset data are often collectedin order to map the disease gene(s). The ages are often (right)censored or truncated, and therefore, many standard techniquesfor linkage analysis cannot be used. In this paper, we presenta correlated frailty model for censored survival data of siblings.The model is used for testing heritability for the age at onsetand linkage between the loci and the gene(s) that influence(s)the survival time. The model is applied to interval-censoredmigraine twin data. Heritability (obtained from the frailtiesrather than actual onset times) was estimated as 0.42; thisvalue was highly significant. The highest lod score, a scoreof 1.9, was found at the end of chromosome 19.  相似文献   
117.
Production of Resveratrol in Recombinant Microorganisms   总被引:3,自引:0,他引:3       下载免费PDF全文
Resveratrol production in Saccharomyces cerevisiae was compared to that in Escherichia coli. In both systems, 4-coumarate:coenzyme A ligase from tobacco and stilbene synthase from grapes were expressed. When p-coumaric acid was used as the precursor, resveratrol accumulations in the culture medium were observed to be comparable in E. coli (16 mg/liter) and yeast (6 mg/liter).  相似文献   
118.
Metabolic mapping of enzyme activities (enzyme histochemistry) is an important tool to understand (patho)physiological functions of enzymes. A new enzyme histochemical method has been developed to detect transketolase activity in situ in various rat tissues and its ultrastructural localization in individual cells. In situ detection of transketolase is important because this multifunctional enzyme has been related with diseases such as cancer, diabetes, Alzheimer's disease, and Wernicke-Korsakoff's syndrome. The proposed method is based on the tetrazolium salt method applied to unfixed cryostat sections in the presence of polyvinyl alcohol. The method appeared to be specific for transketolase activity when the proper control reaction is performed and showed a linear increase of the amount of final reaction product with incubation time. Transketolase activity was studied in liver, small intestine, trachea, tongue, kidney, adrenal gland, and eye. Activity was found in liver parenchyma, epithelium of small intestine, trachea, tongue, proximal tubules of kidney and cornea, and ganglion cells in medulla of adrenal gland. To demonstrate transketolase activity ultrastructurally in liver parenchymal cells, the cupper iron method was used. It was shown that transketolase activity was present in peroxisomes and at membranes of granular endoplasmic reticulum. This ultrastructural localization is similar to that of glucose-6-phosphate dehydrogenase activity, suggesting activity of the pentose phosphate pathway at these sites. It is concluded that the method developed for in situ localization of transketolase activity for light and electron microscopy is specific and allows further investigation of the role of transketolase in (proliferation of) cancer cells and other pathophysiological processes.  相似文献   
119.

Background

The electroencephalography (EEG) is an attractive and a simple technique to measure the brain activity. It is attractive due its excellent temporal resolution and simple due to its non-invasiveness and sensor design. However, the spatial resolution of EEG is reduced due to the low conducting skull. In this paper, we compute the potential distribution over the closed surface covering the brain (cortex) from the EEG scalp potential. We compare two methods – L-curve and generalised cross validation (GCV) used to obtain the regularisation parameter and also investigate the feasibility in applying such techniques to N170 component of the visually evoked potential (VEP) data.

Methods

Using the image data set of the visible human man (VHM), a finite difference method (FDM) model of the head was constructed. The EEG dataset (256-channel) used was the N170 component of the VEP. A forward transfer matrix relating the cortical potential to the scalp potential was obtained. Using Tikhonov regularisation, the potential distribution over the cortex was obtained.

Results

The cortical potential distribution for three subjects was solved using both L-curve and GCV method. A total of 18 cortical potential distributions were obtained (3 subjects with three stimuli each – fearful face, neutral face, control objects).

Conclusions

The GCV method is a more robust method compared to L-curve to find the optimal regularisation parameter. Cortical potential imaging is a reliable method to obtain the potential distribution over cortex for VEP data.
  相似文献   
120.
We present a high-resolution nuclear magnetic resonance (NMR) solution structure of a 14-mer RNA hairpin capped by cUUCGg tetraloop. This short and very stable RNA presents an important model system for the study of RNA structure and dynamics using NMR spectroscopy, molecular dynamics (MD) simulations and RNA force-field development. The extraordinary high precision of the structure (root mean square deviation of 0.3 Å) could be achieved by measuring and incorporating all currently accessible NMR parameters, including distances derived from nuclear Overhauser effect (NOE) intensities, torsion-angle dependent homonuclear and heteronuclear scalar coupling constants, projection-angle-dependent cross-correlated relaxation rates and residual dipolar couplings. The structure calculations were performed with the program CNS using the ARIA setup and protocols. The structure quality was further improved by a final refinement in explicit water using OPLS force field parameters for non-bonded interactions and charges. In addition, the 2′-hydroxyl groups have been assigned and their conformation has been analyzed based on NOE contacts. The structure currently defines a benchmark for the precision and accuracy amenable to RNA structure determination by NMR spectroscopy. Here, we discuss the impact of various NMR restraints on structure quality and discuss in detail the dynamics of this system as previously determined.  相似文献   
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