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11.
R. Finkeldey 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,89(2-3):198-200
The genetic differentiation
within a subdivided population can be partitioned into two proportions, one due to differentiation within sub-populations and the other due to differentiation among subpopulations. A simple mathematical derivation of this procedure, known as Nei's G
ST
-statistics, is presented. The significance of considering the differing relative sizes of subpopulations is stressed. Possible fields of applications for breeders and conservationists who are concerned with the establishment of genetically diverse populations are mentioned. 相似文献
12.
Debbie Truelove Ashfaq Shuaib Sadiq Ijaz Steve Richardson Jay Kalra 《Neurochemical research》1994,19(6):665-671
Repeated ischemic insults at one hour intervals result in more severe neuronal damage than a single similar duration insult. The mechanism for the more severe damage with repetitive ischemia is not fully understood. We hypothesized that the prolonged reperfusion periods between the relatively short ischemic insults may result in a pronounced generation of oxygen free radicals (OFRs). In this study, we tested the protective effects of superoxide dismutase (SOD) and catalase (alone or in combination), and U78517F in a gerbil model of repetitive ischemia. Three episodes (two min each) of bilateral carotid occlusion were used at one hour intervals to produce repetitive ischemia. Superoxide dismutase and catalase were infused via osmotic pumps into the lateral ventricles. Two doses of U78517F were given three times per animal, one half hour prior to each occlusion. Neuronal damage was assessed 7 days later in several brain regions using the silver staining technique. The Mann-Whitney U test was used for statistical comparison. Superoxide dismutase showed significant protection in the hippocampus (CA4), striatum, thalamus and the medial geniculate nucleus (MGN). Catalase showed significant protection in the striatum, hippocampus, thalamus, and MGN and the substantia nigra reticulata. Combination of the two resulted in additional protection in the cerebral cortex. Compared to the controls, there was little protection with a dose of 3 mg/kg of U78517F. There was significant protection with a dose of 10 mg/kg in the hippocampus (CA4), striatum, thalamus, medial geniculate nucleus and the substantia nigra reticulata. The significant protection noted with SOD, catalase or U78517F with repeated ischemia supports, the hypothesis that OFRs may play a role in neuronal damage in repeated cerebral ischemia. 相似文献
13.
N. S. Shekhawat T. S. Rathore R. P. Singh N. S. Deora S. R. Rao 《Plant Growth Regulation》1993,12(3):273-280
Genotype, age of tree, nature of explant and size (length and diameter), season of explant collection, explant position on medium, plant growth regulators and certain additives (ascorbic and citric acids, adenine sulphate, L-arginine, glutamine and ammonium citrate), incubation conditions, and subculturing period greatly influenced the in vitro clonal propagation of P. cineraria. The maximum number of 10–12 shoots were induced from the nodal shoot segment from pruned thorny adult trees on Murashige and Skoog's (MS) medium containing 0.1 mgl-1 indole- 3-acetic acid (IAA)+2.5 mgl-1 benzylaminopurine (BAP)+additives. Higher temperature (31+-2°C) and mixed (fluorescent and incandescent) light of 50 mol m-2 s-1 photon flux density for 12 h per day photoperiod favoured shoot induction and subsequent growth. Explants from thornless trees produced 6–8 shoots per explant on MS medium containing 0.1 mgl-1 IAA+5.0 mgl-1 BAP + additives. Nodal shoot segments obtained from root and stump sprouts produced multiple shoots. Root segments differentiated into multiple shoots on MS medium containing 0.5 mgl-1 indolebutyric acid (IBA)+2.5 mgl-1 BAP.Differentiated shoots multiplied best on MS medium containing 0.1 mgl-1 naphthalene acetic acid (NAA)+1.0 mgl-1 BAP + additives. To yield multiple shoots the original explant was transferred 6 times on fresh medium after harvesting the differentiated shoots. Shoots were rooted by pulsing with 100 mgl-1 IBA for 4 h and then culturing on hormone-free half strength MS medium. Initial dark incubation for 5 days at high temperature (33±2°C) was found essential for root induction from shoots which was 63% within two weeks. The rooted plantlets contained a consistent number of chromosomes (2n=28). It is suggested that the protocol developed could be useful for cloning of mature and tested trees of P. cineraria. 相似文献
14.
This paper presents a simple model for the evolution of reaction norms for age and size at maturity that predicts reaction norms with a variety of shapes. Using realistic parameter values the model predicts reaction norms close to those observed in Drosophila. The major assumptions of the model are: 1) that net reproductive rate is maximized, 2) that growth is determinate, and 3) that mortality rates are independent of age and size at maturity. If, additionally, juvenile mortality is uncorrelated with a growth coefficient, k, the model predicts that selection favors maturation later at a smaller size when k is reduced by environmental factors and that decreased juvenile mortality leads to delayed maturity. These two predictions conform with those found by previous models using other measures of fitness. Correlations between k and juvenile mortality can change the shape of the predicted reaction norm. Depending on the precise form of the correlation, the model can predict done- or bowl-shaped reaction norms and can predict delayed or earlier maturity as k decreases. These shapes are qualitatively different from those predicted by previous models that used different fitness measures. Systematic estimates of the parameter values for this and for related models are required to determine the appropriate fitness measure for models of reaction norms. 相似文献
15.
Heinz Löffler 《Hydrobiologia》1993,264(3):169-174
The northwestern area of the Pannonian Lowland extends into Austria. The climatic and hydrologic attributes of this biographic region promote the existence of extremely astatic bodies water lacking any fish and hence the occurrence of Anostraca, Notostraca, Laevicaudata and Spinicaudata. Zoogeographical and ecological features as well as the extinction of species due to anthropogenic influence are described.Dedicated to Prof. Dr F. Berger, Lunz, Austria, on the occasion of his 90th birthdayDedicated to Prof. Dr F. Berger, Lunz, Austria, on the occasion of his 90th birthday 相似文献
16.
Esterina Pascale Christine Liu Eulalia Valle Karen Usdin Anthony V. Furano 《Journal of molecular evolution》1993,36(1):9-20
Summary All modern mammals contain a distinctive, highly repeated (⩾50,000 members) family of long interspersed repeated DNA called
the L1 (LINE 1) family. While the modern L1 families were derived from a common ancestor that predated the mammalian radiation
∼80 million years ago, most of the members of these families were generated within the last 5 million years. However, recently
we demonstrated that modern murine (Old World rats and mice) genomes share an older long interspersed repeated DNA family
that we called Lx. Here we report our analysis of the DNA sequence of Lx family members and the relationship of this family
to the modern L1 families in mouse and rat. The extent of DNA sequence divergence between Lx members indicates that the Lx
amplification occurred about 12 million years ago, around the time of the murine radiation. Parsimony analysis revealed that
Lx elements were ancestral to both the modern rat and mouse L1 families. However, we found that few if any of the evolutionary
intermediates between the Lx and the modern L1 families were extensively amplified. Because the modern L1 families have evolved
under selective pressure, the evolutionary intermediates must have been capable of replication. Therefore, replicationcompetent
L1 elements can reside in genomes without undergoing extensive amplification. We discuss the bearing of our findings on the
evolution of L1 DNA elements and the mammalian genome. 相似文献
17.
The conservation goal of representation of biodiversity (in the broad sense of all species) in protected areas requires best-possible use of available surrogate information. One standard approach is based on indicator groups of taxa. A minimum set of areas having at least one representation of each indicator species is taken to be representative of other organisms. This same minimum-set approach is adapted to other attributes of biodiversity, for example, derived environmental clusters. A weakness of these approaches is that useful information is lost; for example, for environmental clusters, there is no distinction made either among or within clusters. A more powerful surrogate approach can use some expression of environmental and/or biotic pattern so that variation among areas is seen as part of a continuum rather than partitioned into arbitrary clusters/attributes. The challenge in using pattern effectively is to adopt a robust model for the relationship between pattern and the underlying units of biodiversity, i.e. species. An environmental space (a continuum or ordination pattern), combined with the standard ecological continuum model relating species to environmental space, has advantages over other patterns based on hierarchy or distance matrices. Because an environmental space can be estimated either directly (observed environmental data) or indirectly (data on indicator groups), the corresponding surrogate-measure of biodiversity, environmental diversity (ED) makes best-possible use of either kind of data. We conclude that the arbitrariness of the attribute approach can be replaced by a robust surrogate pattern approach that is flexible and avoids unwarranted assumptions. 相似文献
18.
Mahmood Vahedian Liang Shi Tong Zhu Ronald Okimoto Kathleen Danna Paul Keim 《Plant molecular biology》1995,29(4):857-862
Repetitive DNA sequences comprise a large percentage of plant genomes, and their characterization provides information about both species and genome evolution. We have isolated a recombinant clone containing a highly repeated DNA element (SB92) that is homologous to ca. 0.9% of the soybean genome or about 105 copies. This repeated sequence is tandemly arranged and is found in four or five major genomic locations. FISH analysis of metaphase chromosomes suggests that two of these locations are centromeric. We have determined the sequence of two cloned repeats and performed genomic sequencing to obtain a consensus sequence. The consensus repeat size was 92 bp and exhibited an average of 10% nucleotide substitution relative to the two cloned repeats. This high level of sequence diversity suggests an ancient origin but is inconsistent with the limited phylogenetic distribution of SB92, which is found an high copy number only in the annual soybeans. It therefore seems likely that this sequence is undergoing very rapid evolution. 相似文献
19.
20.
本文报道了虎嘉鱼的生境特点及保护对策,主要是加强宣传教育,严禁滥捕,深入研究,开展人工养殖试验和建立自然保护区等措施,确保物种生存和繁衍。 相似文献