Dr. Stan C. Hokanson
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Browsing Dr. Stan C. Hokanson by Type "Thesis or Dissertation"
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Item Isozyme Variation as Evidence of Gene Flow and Hybridization between Red Oaks Found in an Island Archipelago(1991) Hokanson, Stan C.Isozyme variability was examined in the red oak complex, Quercus subg. Erythrobalanus found on an island archipelago and vicinity in northeastern Wisconsin. Dormant leaf bud samples were collected from Quercus rubra L., Q. ellipsoidalis Hill and their putative hybrids from two peninsula locations and on three islands. Acorns were collected from some of these same trees in three of these locations. Twelve putative loci coding for six enzymes were analyzed. Allele frequency data indicated there was little differentiation between populations. Mean Fst values for the adult trees and acorns were 0.042 and 0.020 respectively. Genetic identities according to Nei ranged from .958 to .999. In spite of these high genetic identities, the populations appeared to be experiencing substantial levels of inbreeding as indicated by positive mean Fit values of 0.183 and 0.373 for the trees and acorns respectively. Estimates of migration rate per generation for the adult trees was 5.70.Item Risk Assessment of Transgenic Plants: Evaluation of Border Rows as a Containment Strategy for Transgenic Pollen and a Comparison of Pollen Dispersal Patterns for Native and Transgenes(1995) Hokanson, Stan C.Despite full commercial approval of twelve transgenic crops in the U.S. (circa 1995), concern is still being expressed regarding the potential risks associated with the agronomic-scale production of transgenic crops. One commonly mentioned concern involves the pollen-mediated escape of engineered genes into populations of crop wild relatives. In this study two questions relevant to this issue were investigated: 1) Can plantings of border rows effectively limit pollen mediated gene movement, and 2) Do the pollen-mediated dispersal patterns of transgenes differ from those of native genes? The ratio of recessive trap plants to wild type donor plants was varied to test the efficacy of border rows as a means to limit the spread of transgenic pollen to discontiguous satellite plots. Gene movement within the border plots assumed a leptokurtic distribution. Increasing the number of donor plants increased levels of gene flow both within the border and to the discontiguous satellite plots. As the trap/donor ratio increased, there was a significant decrease in long distance gene movement to the satellites, although the observed year to year and site to site variability could limit the effectiveness of this strategy. Furthermore, extremely large numbers of border plants would be required to minimize pollen movement on a commercial scale. Dispersal patterns of transgenes and native genes were evaluated by comparing levels of pollen-mediated gene movement from melon plants (Cucumis melo) expressing dominant morphological and transgenic marker genes into a surrounding border of recessive non-transgenic melon plants. Long distance dispersal patterns for the two genes were identical and dispersal patterns into the plot borders were nearly identical. Several of the apparent discrepancies were explained by transgene inactivation, a phenomenon which has implications for any study measuring gene movement with transgenic plants. Results from this study validate the assumption that native and transgenes have the same dispersal patterns. Thus, application of non-transgenic results to trans gene escape and dispersal issues should be appropriate. However, the assessment of establishment and spread will depend on both pollen movement and the fitness value of the particular transgene crop combination.