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21.
22.
Hans Peter Comes Joachim W. Kadereit Andreas Pohl Richard J. Abbott 《Plant Systematics and Evolution》1997,206(1-4):375-392
Chloroplast DNA (cpDNA) and isozyme variation were analyzed over a range of populations of two infraspecific taxa of the tetraploidSenecio vulgaris. The isozyme data were supportive of the hypothesis that the weedy and cosmopolitanS. vulgaris var.vulgaris is an evolutionary derivative ofS. vulgaris subsp.denticulatus from the coasts of W Europe and montane altitudes in S Spain and Sicily. The two taxa exhibited a very high genetic identity with subsp.denticulatus containing slightly more isozyme diversity than was found in var.vulgaris. — Three cpDNA haplotypes (A, B, C) already known from other Mediterranean diploid species ofSenecio were resolved in var.vulgaris, and an additional fourth haplotype (E) was found in subsp.denticulatus. Two alternative hypotheses were chosen to account for the origin and maintenance of the observed cpDNA composition ofS. vulgaris. It either reflects (1) the retention of an ancestral polymorphism which stems from the recurrent and polytopic formation of ancestral tetraploid lineages; or (2)S. vulgaris originally was characterized by haplotype E, and haplotypes A, B and C were acquired through repeated introgressive hybridization with related diploid species. The finding that very low levels of nuclear (isozyme) diversity were present in both taxa ofS. vulgaris examined supports the second of these two hypotheses; however, more detailed analysis of nuclear genetic diversity is required before a firm conclusion can be reached on this matter.Dedicated to emer. Univ.-Prof. DrFriedrich Ehrendorfer on the occasion of his 70th birthday 相似文献
23.
David J Lee Lewis EH Bingle Karin Heurlier Mark J Pallen Charles W Penn Stephen JW Busby Jon L Hobman 《BMC microbiology》2009,9(1):252
Background
Homologous recombination mediated by the λ-Red genes is a common method for making chromosomal modifications in Escherichia coli. Several protocols have been developed that differ in the mechanisms by which DNA, carrying regions homologous to the chromosome, are delivered into the cell. A common technique is to electroporate linear DNA fragments into cells. Alternatively, DNA fragments are generated in vivo by digestion of a donor plasmid with a nuclease that does not cleave the host genome. In both cases the λ-Red gene products recombine homologous regions carried on the linear DNA fragments with the chromosome. We have successfully used both techniques to generate chromosomal mutations in E. coli K-12 strains. However, we have had limited success with these λ-Red based recombination techniques in pathogenic E. coli strains, which has led us to develop an enhanced protocol for recombineering in such strains. 相似文献24.
25.
26.
Aim Our goals were: (1) to investigate patterns of genetic variation in the French Massif Central (MC) of Soldanella alpina (Primulaceae), an alpine plant species that has only one known population in the region; (2) to analyse these patterns in order to deduce the Quaternary history of the population and to predict how current climatic warming may affect it; and (3) to review molecular analyses from the MC to evaluate the importance of the region for the conservation of genetic diversity. Location Europe, with a special focus on the French Massif Central and adjacent regions. Methods Amplified fragment length polymorphisms (AFLPs) were analysed for 192 individuals (nine populations) of S. alpina (subsp. alpina) representing the MC, Pyrenees and south‐western Alps. Population genetic diversity was assessed by various parameters (e.g. HE, Shannon’s I). Neighbor‐Net and Bayesian approaches, and analysis of molecular variance (AMOVA) were used to infer population genetic relationships and structure. Results Individuals generally clustered according to populations within mountain regions. Hierarchical AMOVA indicated significant variation among mountain ranges (33.2% of the total variance), but there was also strong differentiation between populations (26.3%). The single population of S. alpina from the MC was identified as a distinct lineage of high genetic diversity. Our literature survey indicated that taxa with low and with high genetic diversity exist in the MC, and that genetic relationships to surrounding regions are diverse. Main conclusions The high genetic diversity and distinctiveness of S. alpina in the MC suggests the long‐term persistence of the single population in this region, which might have been favoured through elevational range shifts in response to past climatic change. This interpretation partly accords with other studies indicating that several plant and animal populations in the MC contain comparatively high genetic diversity, represent genetically independent lineages, and/or are likely descendants of populations that persisted in the MC throughout the Quaternary. These data underline the conservation importance of the MC as a key area for the long‐term persistence of species with often high levels of intraspecific genetic diversity. 相似文献
27.
JW Santo Domingo J C Radway E W Wilde P Hermann T C Hazen 《Journal of industrial microbiology & biotechnology》1997,18(6):389-395
Immobilization of the trichloroethylene-degrading bacterium Burkholderia cepacia was evaluated using hydrophilic polyurethane foam. The influence of several foam formulation parameters upon cell retention
was examined. Surfactant type was a major determinant of retention; a lecithin-based compound retained more cells than pluronic-
or silicone-based surfactants. Excessive amounts of surfactant led to increased washout of bacteria. Increasing the biomass
concentration in the foam from 4.8 to 10.5% dry weight per wet weight of foam resulted in fewer cells being washed out. Embedding
at reduced temperature did not significantly affect retention, while the use of a silane binding agent gave inconsistent
results. The optimal formulation retained all but 0.2% of total embedded cells during passage of 2 L of water through columns
containing 2 g of foam. All foam formulations tested reduced the culturability of embedded cells by several orders of magnitude,
but O2 consumption and CO2 evolution rates of embedded cells were never less than 50% of those of free cells. Nutrient amendments stimulated an increase
in cell volume and ribosomal activity in immobilized cells as indicated by hybridization studies using fluorescently labeled
ribosomal probes. These results indicate that, although immobilized cells were mostly nonculturable, they were metabolically
active and thus could be used for biodegradation of toxic compounds.
Received 23 December 1996/ Accepted in revised form 13 March 1997 相似文献
28.
Restriction-map variation associated with the G6PD polymorphism in natural populations of Drosophila melanogaster 总被引:10,自引:0,他引:10
Restriction-map variation was studied in 126 copies of the G6pd region in X
chromosome lines of Drosophila melanogaster from North America, Europe, and
Africa. Special attention was focused on the distribution of variation
relative to the geographically variable polymorphism for two
electrophoretic variants. Nucleotide heterozygosity as determined by eight
six-cutter restriction enzymes for the 13-kb region is estimated, on the
basis of the worldwide sample, to be 0.065%, which is the lowest value
reported for any comparable region in the D. melanogaster genome.
Significant linkage disequilibrium between electrophoretic alleles and
restriction-site variation is observed for several sites. In contrast to
published studies of other genetic regions, there are large insertions that
reach significant frequencies and are found across considerable geographic
distances. There is a clustering of this variation inside the first large
intervening sequence of the G6PD gene.
相似文献
29.
Joachim W. Kadereit 《Plant Systematics and Evolution》1984,145(1-2):135-153
Senecio vulgaris L. (2n = 40) is suggested to be of autotetraploid origin fromS. vernalis
Waldst. & Kit. (2n = 20). This conclusion is based on results obtained from experimental hybridisations and cytological observations, and the consideration of morphological affinities, patterns of geographical distribution and hybrid formation under natural conditions. The morphological differences between the two species are related to a difference in the breeding system. WhilstS. vernalis is self-incompatible,S. vulgaris is self-compatible and strongly self-pollinating. Equally, other self-pollinating taxa traditionally associated withS. vulgaris are shown to have evolved independently from outbreeding relatives. Within a narrow frame of relationship, annual weeds have evolved in different cytotaxonomic circumstances. 相似文献
30.
Aim We investigate the geographical genetic structure of two coastal plant species, Cakile maritima Scop. (Brassicaceae) and Eryngium maritimum L. (Apiaceae), through three sea straits and along one continuous stretch of coast using amplified fragment length polymorphisms (AFLPs). The two species have a similar ecology in that they grow in sandy habitats, but differ in life‐form (annual vs. perennial) and dispersability of seeds by sea water as inferred from floating experiments. The sea straits differ in their geological history and their modern current systems. The primary goal of our study was to test the hypothesis that sea straits have an influence on the geographical patterns of genetic variation at the population level. Location The areas around the Strait of Gibraltar, the Dardanelles, the Bosporus and the Atlantic coast of western France. Methods For both species we investigated AFLP variation in several populations from each area. Bayesian clustering and diversity and differentiation measures were used to analyse the genetic data. Results In most areas the spatial genetic structure was similar between the two species. They share the presence of distinct genetic gaps along the coast through the Strait of Gibraltar and the Bosporus, and these genetic gaps coincide with the straits. Both species show genetic continuity along the coast of western France. A distinct genetic gap was found through the Dardanelles for C. maritima but not for E. maritimum. Main conclusions The study shows that sea straits have an influence on the geographical patterns of genetic variation. Sea currents are inferred to cause the genetic gap through the Strait of Gibraltar. In the Bosporus and, for C. maritima, through the Dardanelles, the genetic gaps found are explained by the past closure of these two straits as well as by present‐day factors. Simulations indicate that the lower differentiation of C. maritima through the Dardanelles than through the Bosporus cannot be explained by the difference in geological history of these two straits. The difference in seed dispersability between the two species is argued to be responsible for the observation that differentiation among genetic clusters is higher in E. maritimum than in C. maritima where a direct comparison is possible. 相似文献