Molecular evolution in natural populations of Skeletonema costatum: Restriction mapping and analysis of the chloroplast genome.
Item
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Title
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Molecular evolution in natural populations of Skeletonema costatum: Restriction mapping and analysis of the chloroplast genome.
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Identifier
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AAI9510724
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identifier
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9510724
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Creator
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Stabile, Joseph E.
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Contributor
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Advisers: Jane Gallagher | Eleanore Wurtzel
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Date
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1994
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Botany | Biology, Oceanography
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Abstract
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A wealth of background information on the ecology, physiology and population genetics of the marine diatom Skeletonema costatum makes this a unique model system in phytoplankton because new molecular genetic data can be compared with prior results. The genetic divergence among 29 isolates representative of Narragansett Bay populations of S. costatum was quantified using restriction analysis of chloroplast DNA (cpDNA). CpDNA data were compared to earlier results obtained using allozymes in order to study the process of speciation in this genetically diverse and widely distributed species. Data from terrestrial plants indicates that cpDNA evolves more slowly than allozymes and provides markers useful for the detection of genetic relationships over higher phylogenetic levels. The pattern of cpDNA variation in Skeletonema spp. was investigated to determine if this general relationship is also true of chromophytes.;The chloroplast genome of S. costatum is 131 kilobases (Kb). Its organization is typical of most plants in that an inverted repeat separates a large and small single copy region. Chloroplast DNA restriction site maps of two strains representative of the most diverse allozyme groups, reveal that their are extensive restriction site polymorphisms, but no major rearrangements among their cpDNAs. Most observed differences appear to be the result of restriction site mutations. The colinearity of these chloroplast genomes indicates that restriction analysis of chloroplast DNA is appropriate for studying lower phylogenetic relationships in diatoms.;Five homologous cpDNA probes were used to observe restriction fragment length polymorphisms (rflps) among the 29 Narragansett Bay isolates, 3 strains of S. costatum isolated from other areas and 2 strains of a sister taxon S. tropicum. The pattern of divergence observed among all Skeletonema spp. suggests that the distribution of chloroplast lineages follows a relationship based on a light and thermal gradient. Among the Narragansett Bay isolates, there is a strong concordance of pattern between the cpDNA and allozyme data. However, the overall genetic diversity observed with the allozyme data is greater than that of the cpDNA rflps, confirming the hypothesis that cpDNA evolves more slowly in diatoms as well as in terrestrial plants.;Both cpDNA and allozyme data suggest that there is limited gene flow between the most diverse allozyme groups in Narragansett Bay. Analysis of the chloroplast and allozyme data sets within the theoretical framework of the phenetic, biological and phylogenetic species concepts suggests that all strains from Narragansett Bay are one species. The observed pattern of divergence among the Narragansett Bay populations suggests that they are probably in the incipient stages of speciation. However, more data on the extent and pattern of gene flow are needed to confirm this conclusion.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
