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  • Electronic Resource  (3)
  • 1990-1994  (3)
  • Allozymes  (2)
  • 73.40.Lq
  • Electron transfer
  • Polymer and Materials Science
Material
  • Electronic Resource  (3)
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Year
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 80 (1990), S. 635-640 
    ISSN: 1432-2242
    Keywords: Pinus ; Species hybridization ; Allozymes ; Evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Allozyme differentiation at 13 loci was studied in populations of Pinus tabulaeformis, P. densata, and P. yunnanensis from China. It was previously suggested that P. densata represents a Tertiary hybrid between P. tabulaeformis and P. yunnanensis. The observed levels of allozyme variation within and among the investigated species were comparable to those of other conifers. P. tabulaeformis differed markedly from P. yunnanensis with respect to allozyme frequencies, while P. densata was intermediate between the two putative parents. There was evidence of homozygote excess in embryos from all investigated species, as compared to Hardy-Weinberg expectations. The observed allozyme composition of P. densata conformed to earlier morphological and molecular evidence indicating hybrid origin of this taxon. It was proposed that fusion of gene pools from P. tabulaeformis and P. yunnanensis has led to adaptive evolution of a new species, P. densata.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 86 (1993), S. 159-165 
    ISSN: 1432-2242
    Keywords: Allozymes ; Chloroplast DNA ; Introgression ; Evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Allozyme variation was examined in 22 populations of Pinus densiflora (Sieb, et Zucc.) and four geographic varieties of P. sylvestris (L.): var ‘lapponica’ (Fries, Hartman), var ‘armena’ (Komarov), var ‘mongolica’ (Litvinov) and var ‘sylvestriformis’ (Takenouchi). In addition, we developed paternal chloroplast (cp) DNA markers that distinguish P. densiflora from var ‘lapponica’, var ‘armena’ and var ‘mongolica’. UPGMA cluster analysis based on Nei's distances between all pairwise combinations of the 22 populations revealed patterns corresponding strictly to geographic origin and taxonomic status. Analysis of allozyme variation in var ‘lapponica’, var ‘armena’ and var ‘mongolica’ demonstrated a high level of intrapopulational variability but a low level of interpopulational differentiation. It appears that the late Pleistocene blending of genetically diverse populations was responsible for the observed variation patterns. The constructed phylogenetic trees also showed late divergence of these three varieties. The var ‘sylvestri formis’ was genetically distinct from the other three P. sylvestris varieties. The genetic distances separating var ‘sylvestriformis’ from P. densiflora and the other taxa lend support to a separate taxonomic status for var ‘sylvestriformis’ and a close relation with P. densiflora. We found that var ‘sylvestriformis’ harbors admixtures of allozymes and cpDNA from both P. sylvestris and P. densiflora, which suggests an introgressive nature of this variety. Levels of intrapopulational variability were similar in P. sylvestris and P. densiflora, but interpopulational differentiation was much higher in P. densiflora. In the constructed phylogenetic trees, populations of this species were characterized by relatively long internode distances and branch lengths. The present results suggest that P. densiflora has a more advanced evolutionary age than P. sylvestris.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 49 (1993), S. 2179-2188 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The kinetics of methyl methacrylate (MMA) polymerization, and of its copolymerization with various acrylates, at high conversions in the presence of a chain transfer agent, are investigated with a dilatometer over the entire course of reaction. The displacement to higher conversions of the onset of the gel effect in the MMA homopolymerization, in the presence of a chain transfer agent, was determined. Similar information is also provided for the MMA-acrylate copolymerization systems. An increase in polymerization temperature slightly delays the onset of the gel effect in the MMA-acrylate copolymerization, but considerably increases the final conversion. The final conversion in copolymerization for a constant concentration of the chain transfer agent is independent of the initiator concentration, but is a function of the polymerization temperature. The reaction time for reaching the limiting conversion in copolymerization is increased with an increasing amount of the second monomer, as well as with an increasing number of carbon atoms in the acrylate used as the second monomer. © 1993 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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