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41.
核型似近系数的聚类分析方法 总被引:14,自引:0,他引:14
本文根据近年来核型分析所积累的大量资料,以及谭远德(1991)提出的似近分析理论,提出了核型似近系数A聚类分析方法,确定了核型计算公式,井应用于lo种淡水鱼核型似近系数聚类分析,获得了与形态分类学非常一致的结果。此外,还提出了染色体带型计算公式,从而使核型公式和校型似近系数从核型的整体结构、染色体形态结构和染色体内部结构等三个层次上,较精确地刻画了物种核型特性和物种间校型的等同性或同源性。以此核型似近系数作为分类依据所获得的物种分类结果,能真实地和客观地反映物种的自然分类模式。 相似文献
42.
Ephedra sinica is a rare and vulnerable species in China, and the habitat of Ephedra sinica is seriously threatened (by climate change and human activities). Predicting the suitable growth areas and constructing ecological corridors for Ephedra sinica in China will help to protect it scientifically. Based on 306 valid distribution records and 13 selected environmental factors, the maximum entropy (MaxEnt) model was used to simulate the potential current habitat zones and future (2050 and 2070) habitat zones of Ephedra sinica under four climate change scenarios. The minimum cumulative resistance (MCR) model was applied to extract important ecological corridors of Ephedra sinica. The results indicate that: (1) Under the current environment, the total area of the suitable habitat for Ephedra sinica in China is 42.24 × 105 km2, mainly distributed in Northwest China and North China. (2) Suitable area increases as the RCP rises. The center of mass of the habitat zone moved northward from Shaanxi Province to Ordos City in Inner Mongolia Autonomous Region. (3) Of the 13 environmental factors selected, the primary factor was elevation (20.8 %), followed by wettest month precipitation (18.2 %) and temperature seasonality (15.2 %). (4) Built 19 ecological corridors, with a total corridor length of 430.2 km, including seven long-distance passages and 12 short-distance corridors. All corridors are far from the artificial surface, mostly near high-altitude areas. The 19 ecological corridors constructed using the MCR model will also provide considerable importance for the survival of Ephedra sinica on a longer time scale in the future. 相似文献
43.
The difference in reduction potentials between ortho and para-benzoquinones has been calculated. The employs gas phase ab initio and semi-empirical computations in combination with free energy perturbation theory applied to gas and solution phase Monte Carlo simulations. The effects on calculated results of altering solute electrostatic parameterisation in solution phase simulations is examined. Atom centred charges derived from the molecular electrostatic potentials, MEPs, from optimised ab initio wavefunctions and charges generated by consideration of hydrogen bonded complexes are considered. Parameterisation of hydroxyl torsions in hydroquinone molecules is treated in a physically realistic manner. The coupled torsional system of the ortho-hydrobenzoquinone molecule is described by a potential energy surface calculated using gas phase AM1 semi-empirical computations rather than the simple torsional energy functions frequently employed in such calculations. Calculated differences in electrode potentials show that the electrostatic interactions of quinone and hydroquinone molecules in aqueous solution are not well described by atom centred charges derived from ab initio calculated MEPs. Moreover, results in good agreement with the experimental reduction potential difference can be obtained by employing high level ab initio calculations and solution phase electrostatic parameters developed by consideration of hydrogen bonded complexes. 相似文献
44.
关中小麦品种产量构成因素的相互关系和产量育种目标 总被引:7,自引:0,他引:7
对关中地区不同年代及当前大面积推广的小麦品种(系)的产量及其构成因素进行了遗传分析和通径分析。结果表明:陕西关中地区近期小麦品种的产量育种目标的趋势是在提高现有穗粒数的基础上,保持现有的穗数(700万/hm^2)及千粒重(38g左右),以求在提高品种产量潜力的同时,保持或增加品种的稳定性能;或是大幅度提高穗粒数(35粒左右),适当提高千粒重(40g左右),适当降低穗数(600万/hm^2左右),以 相似文献
45.
中国种子植物区系定量化研究 V.区系相似性 总被引:3,自引:0,他引:3
本文总结了应用相似系数即关联系数进行植物区系相似性分析的现状,指出了存在的问题.然后,从集合论角度讨论了区系相似性、相似关系及其相似系数的实质.作者以为在区系相似性分析中应用R.R.Sokal和C.D.Michener(1958)提出的简单匹配系数比较适宜,同时亦能避免以往区系相似性分析中缺乏可比性及某些“表相”相似等问题.最后,还提出了总体相似系数和类型相似系数二个新概念,以便按照吴征镒教授关于中国植物区系研究的学术思想统一研究各个不同地区植物区系的相似性.对此,作者用了6个区系实例进行了演算说明. 相似文献
46.
47.
M J DE. MAINE 《The Annals of applied biology》1995,127(1):151-156
Dihaploids obtained from a somatically chromosome-doubled dihaploid potato were crossed with Solanum phureja clones. To test the effect of inbreeding, measurements were made of their seed production and the tuber yield, tuber number and mean tuber weight of their offspring. On average, seed production of the second generation dihaploids was higher than that of the original dihaploid progenitor. Progeny tuber yield and its components were little different from those of the original dihaploid's progeny. Tuber flesh quality, as measured lack of blemishes, was better in the offspring of second generation dihaploids.
It is suggested that the negative effects of producing second generation dihaploids are minor compared with producing the first generation dihaploid from a tetraploid, because most deleterious recessives have already been unmasked. The results indicated residual variation within the original dihaploid which could be exploited for plant breeding purposes.
An indicator of inbred status, alternative to the inbreeding coefficient, is suggested which could be applied to both diploids and tetraploids. 相似文献
It is suggested that the negative effects of producing second generation dihaploids are minor compared with producing the first generation dihaploid from a tetraploid, because most deleterious recessives have already been unmasked. The results indicated residual variation within the original dihaploid which could be exploited for plant breeding purposes.
An indicator of inbred status, alternative to the inbreeding coefficient, is suggested which could be applied to both diploids and tetraploids. 相似文献
48.
Summary Proton chemical shifts of a series of disordered linear peptides (H-Gly-Gly-X-Gly-Gly-OH, with X being one of the 20 naturally
occurring amino acids) have been obtained using 1D and 2D 1H NMR at pH 5.0 as a function of temperature and solvent composition. The use of 2D methods has allowed some ambiguities in
side-chain assignments in previous studies to be resolved. An additional benefit of the temperature data is that they can
be used to obtain ‘random coil’ amide proton chemical shifts at any temperature between 278 and 318 K by interpolation. Changes
of chemical shift as a function of trifluoroethanol concentration have also been determined at a variety of temperatures for
a subset of peptides. Significant changes are found in backbone and side-chain amide proton chemical shifts in these ‘random
coil’ peptides with increasing amounts of trifluoroethanol, suggesting that caution is required when interpreting chemical
shift changes as a measure of helix formation in peptides in the presence of this solvent. Comparison of the proton chemical
shifts obtained here for H-Gly-Gly-X-Gly-Gly-OH with those for H-Gly-Gly-X-Ala-OH [Bundi, A. and Wüthrich, K. (1979) Biopolymers, 18, 285–297] and for Ac-Gly-Gly-X-Ala-Gly-Gly-NH2 [Wishart, D.S., Bigam, C.G., Holm, A., Hodges, R.S. and Sykes, B.D. (1995) J. Biomol. NMR, 5, 67–81] generally shows good agreement for CH protons, but reveals significant variability for NH protons. Amide proton chemical
shifts appear to be highly sensitive to local sequence variations and probably also to solution conditions. Caution must therefore
be exercised in any structural interpretation based on amide proton chemical shifts. 相似文献
49.
低高径比喷射环流生化反应器流体力学和发酵性能的研究 总被引:5,自引:0,他引:5
对高径比s≤2.5喷射环流生化反应器的流体力学和传质特性进行了系统的研究,选出反应器的最佳结构,关联出氧的体积传递系数(kLa)表达式。在此基础上,进行了谷氨酸发酵试验,摸索出用该设备进行各氨酸发酵的最佳工艺条件,使5批一次性投糖发酵的糖酸转化率达到50%以上。 相似文献
50.