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11.
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杂交试验是一项费时费钱的工作,因此在进行试验之前如能进行严密的设计,给出试验所需的样本大小是十分必要的,统计学中常见的估计样本容理的公式不宜应用于杂交试验,本文分两种情况给出了杂交试验中样本容量的估计公式,据此估计出的样本容量安排杂交试验,可在满足试验者要求的条件下,使试验的总成本最低或使试畜的总头数最少。 相似文献
13.
Stomach contents of 112 bycaught harbor porpoises ( Phocoena phocoena ) collected between 1989 and 1996 in the Kattegat and Skagerrak seas were analyzed to describe diet composition and estimate prey size, to examine sample size requirements, and to compare juvenile and adult diets. Although porpoises preyed on a variety of species, only a few contributed substantially to the diet. Atlantic herring ( Clupea harengus ) was the dominating prey species for both juveniles and adults. Our results, in combination with those from previous studies, suggest that where herring is a dominant food source, porpoises prey primarily on size classes containing mature or maturing individuals. Further, we also show that Atlantic hagfish ( Myxine glutinosa ) may be an important food resource, at least for adult porpoises. Examination of sample size requirement showed that, depending on the taxonomic level used to describe the diet, a minimum of 35–71 stomachs are needed to be confident that all common prey species will be found. 相似文献
14.
F J Livesey 《Briefings in Functional Genomics and Prot》2003,2(1):31-36
One of the critical limitations of current microarray technologies for use in expression analyses is the relatively large amount of input RNA required to generate labelled cDNA populations for array analysis. In situations where RNA is limiting, the options for expression profiling are to increase cDNA labelling and hybridisation efficiency, or to use an amplification strategy to generate enough RNA/cDNA for use with a standard labelling method. Sample amplification approaches must preserve the representation of the relative abundances of the different RNAs within the starting population and must also be highly reproducible. This review evaluates current signal and sample amplification technologies, including those that can be used to generate labelled cDNA populations for array analysis from as little as a single cell. 相似文献
15.
Insights into the local residual entropy of proteins provided by NMR relaxation. 总被引:4,自引:3,他引:1 下载免费PDF全文
Z. Li S. Raychaudhuri A. J. Wand 《Protein science : a publication of the Protein Society》1996,5(12):2647-2650
A simple model is used to illustrate the relationship between the dynamics measured by NMR relaxation methods and the local residual entropy of proteins. The expected local dynamic behavior of well-packed extended amino acid side chains are described by employing a one-dimensional vibrator that encapsulates both the spatial and temporal character of the motion. This model is then related to entropy and to the generalized order parameter of the popular "model-free" treatment often used in the analysis of NMR relaxation data. Simulations indicate that order parameters observed for the methyl symmetry axes in, for example, human ubiquitin correspond to significant local entropies. These observations have obvious significance for the issue of the physical basis of protein structure, dynamics, and stability. 相似文献
16.
Donald M. Gray Dimitrij Lang Ekkehard Kuner Marilyn Vaughan John Sutherland 《Analytical biochemistry》1984,136(1):247-250
The design of a thin quartz cell suitable for absorption and circular dichroism measurements in the vacuum ultraviolet is described. Important features of the cell are (1) that it can be disassembled for cleaning and reproducibly reassembled with path lengths up to 0.3 mm, and (2) that strain in the windows from the compressed sample can be relieved by a sample overflow port. The latter feature allows the cell to be used for circular dichroism as well as absorption measurements. 相似文献
17.
Analysis of contingency tables under cluster sampling 总被引:2,自引:0,他引:2
18.
Determination of window size for analyzing DNA sequences 总被引:4,自引:0,他引:4
Fumio Tajima 《Journal of molecular evolution》1991,33(5):470-473
Summary DNA sequences are generally not random sequences. To show such nonrandomness visually, DNA sequence data are often plotted as moving averages for a certain length of window slid along a sequence. Here a simple algorithm is presented for determining the window size and for finding a nonrandom region of sequence. 相似文献
19.
Information-theoretical entropy as a measure of sequence variability. 总被引:11,自引:0,他引:11
We propose the use of the information-theoretical entrophy, S = -sigman pi log2 pi, as a measure of variability at a given position in a set of aligned sequences. pi stands for the fraction of times the i-th type appears at a position. For protein sequences, the sum has up to 20 terms, for nucleotide sequences, up to 4 terms, and for codon sequences, up to 61 terms. We compare S and Vs, a related measure, in detail with Vk, the traditional measure of immunoglobulin sequence variability, both in the abstract and as applied to the immunoglobulins. We conclude that S has desirable mathematical properties that Vk lacks and has intuitive and statistical meanings that accord well with the notion of variability. We find that Vk and the S-based measures are highly correlated for the immunoglobulins. We show by analysis of sequence data and by means of a mathematical model that this correlation is due to a strong tendency for the frequency of occurrence of amino acid types at a given position to be log-linear. It is not known whether the immunoglobulins are typical or atypical of protein families in this regard, nor is the origin of the observed rank-frequency distribution obvious, although we discuss several possible etiologies. 相似文献
20.