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  • 1
    ISSN: 1432-1432
    Keywords: Sea urchin ; Actin genes ; Gene conversion ; DNA sequence ; Muscle actin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We report the nucleotide sequence of the single muscle actin gene of the sea urchinStrongylocentrotus purpuratus. Comparison of the protein-coding sequence of this muscle actin gene (pSpG28) with that of two linked sea urchin cytoskeletal actin genes (pSpG17 and CyIIa) reveals a region of exceptional sequence conservation from codon 61 through codon 120. Furthermore, when silent nucleotide changes are compared, the conservation of this region is still evident (7.9% silent site differences in the conserved region vs 43.3% silent site differences in the rest of the gene when pSpG28 and CyIIa are compared), indicating that the conservation is not due to particularly stringent selection on the portion of the protein encoded by this region of the genes. These observations suggest that a gene conversion has occurred between the muscle actin gene and a cytoskeletal actin gene recently in the evolution of the sea urchin genome. Gene conversion between nonallelic actin genes may thus play a role in maintaining the homogeneity of this highly conserved gene family.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5052
    Keywords: Basalt ; Deciduous woodland ; Diversity ; Reciprocal averaging ; Size structure ; Stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Multivariate models based independently on the floristic and environmental attributes of sample quadrats from an escarpment woodland, were constructed. They were used to interpret the ecology of plant species distribution and to investigate the size structure of tree populations. Site instability, soil water status, and past management and grazing pressure were found to exert major influences on the composition and structure of the woodland. It is suggested that early mortality associated with site instability, plays an important role in maintaining the floristic diversity of vascular plants in the woodland ground flora, by increasing the frequency of tree replacement. This may have the effect of preventing canopy closure and any associated, detrimental effects of low light intensities. The relevance of the work of the conservation management of escarpment woods in Northern Ireland is discussed.
    Type of Medium: Electronic Resource
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