Safety of Genetically Engineered Foods Approaches to Assessing Unintended Health Effects (2004) / Chapter Skim
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2 Methods and Mechanisms for Genetic Manipulation of Plants
2 Methods and Mechanisms for Genetic Manipulation of Plants
Pages 23-38
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From page 23... ...
These changes, along with natural evolutionary changes, have resulted in common food species that are now genetically different from their ancestors. Advantageous outcomes of these genetic modifications include increased food production, reliability, and yields; enhanced taste and nutritional value; and decreased losses due to various biotic and abiotic stresses, such as fungal and bacterial pathogens.
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PLANT GENETIC MODIFICATION Techniques Other than Genetic Engineering Simple Selection The easiest method of plant genetic modification (see Operational Definitions in Chapter 1) , used by our nomadic ancestors and continuing today, is simple selection.
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Because of the random nature of recombining genes and traits in crossed plants, breeders usually have to make hundreds or thousands of hybrid progeny to create and identify those few that possess useful features with a minimum of undesirable features. For example, the majority of progeny may show the desired disease resistance, but unwanted genetic features of the disease-resistant parent may also be present in some.
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From page 26... ...
In somatic hybridization, a process also known as cell fusion, cells growing in a culture medium are stripped of their protective walls, usually using pectinase, cellulase, and hemicellulase enzymes. These stripped cells, called protoplasts, are pooled from different sources and, through the use of varied techniques such as electrical shock, are fused with one another.
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From page 27... ...
Once a useful mutation is identified, breeders work to reduce the deleterious mutations or other undesirable features of the mutated plant. Nevertheless, crops derived from mutation breeding still are likely to carry DNA alterations beyond the specific mutation that provided the superior trait.
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Like somaclonal variation, cell selection has largely been superceded by recombinant technologies because of their greater precision, higher rates of success, and fewer undocumented mutations. Genetic Engineering As noted in Chapter 1, this report defines genetic engineering specifically as one type of genetic modification that involves an intended targeted change in a plant or animal gene sequence to effect a specific result through the use of rDNA technology.
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By substituting the DNA of interest for the crown gall disease-causing DNA, scientists derived new strains of Agrobacterium that deliver and stably integrate specific new genetic material into the cells of target plant species. If the transformed cell then is regenerated into a whole fertile plant, all cells in the progeny also carry and may express the inserted genes.
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Barbara McClintock first described such transposable elements in corn plants during the 1950s (Cold Spring Harbor Laboratory, 1951)
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Techniques Fundamental to Genetic Engineering in Livestock Although the following are not methods to generate modifications per se, they are considered modern methods that support the overall breeding and selection system for propagating desired genotypes for animals expressing desired traits. Embryo Recovery and Transfer and Superovulation Embryo recovery and transfer allow valuable animals to contribute more offspring to the gene pool (Seidel, 1984)
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using embryonic stem cell lines in early embryos; and 5. manipulating cultured somatic cells to transfer their nuclei into enucleated oocytes.
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. Retroviral Vectors This method is similar to viral delivery methods used in plants in that virus strains are modified to carry genetic material into a cell.
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Initially animals will be screened for genes that control simple traits that may be undesirable, such as horns in cattle or metabolic stress syndrome in pigs. In time, easily identifiable markers that accompany multiple genes controlling more complex traits, such as meat tenderness and taste, growth, offspring size, and disease resistance, will become available to improve animal health and production traits (Dekkers and Hospital, 2002)
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From page 35... ...
. Traditional genetic modification methods that have been employed -- particularly for microbial starter cultures -- include selection, mutagenesis, conjugation, and protoplast fusion, the last of which is analogous to somatic hybridization in plant systems.
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The most common method used to introduce recombinant DNA into microorganisms is transformation, whereby DNA of interest is introduced directly into recipient cells by making them permeable using chemical agents, enzymes, or electroporation. The first method developed for LAB was plasmid protoplast fusion, in which recipient cells are stripped of walls and subsequently fused with polyethylene glycol, trapping the newly introduced DNA between the cells (Kondo and McKay, 1984)
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Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press.
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1986. Intergeneric hybrids of Saccharomyces cerevisiae and Zygosaccharomyces fermentati obtained by protoplast fusion.
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