Environmental Effects of Transgenic Plants The Scope and Adequacy of Regulation (2002) / Chapter Skim
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1 Ecological, Genetic, and Social Factors Affecting Environmental Assessment of Transgenic Plants
1 Ecological, Genetic, and Social Factors Affecting Environmental Assessment of Transgenic Plants
Pages 17-51
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From page 17... ...
As the twentieth century progressed, the impacts of agricultural practices on human health and the environment became a focus of public attention (e.g., Carson 1962~. Regulations and incentive programs were developed for agriculture and now have a major influence on farming, ranging from the choice of tillage practices to the choice of pest control techniques.
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For example, it is clear that environmental standards being developed for transgenic plant cultivars consider impacts that were rarely even measured when novel conventional crop cultivars were introduced
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In its current form, the coordinated framework gives the USDA the lead role in assessing the potential effects of nonpesticidal transgenic plants on other plants and animals in both agricultural and nonagricultural environments. The EPA takes the lead role in assessing the health and environmental effects of plants engineered to produce pesticidal substances, and the FDA leads the review of potential health effects of nonpesticidal transgenic plants.
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There has been much debate about the potential for genetic modification of crops to cause environmental impacts of a magnitude similar to that caused by the introduction of completely new species. Therefore, the next section of this chapter presents information on the history of environmental effects of conventional crop breeding compared to that of introduced species and also examines the hypothesis that the degree of environmental risk is related to the number of genetic changes introduced into an ecosystem.
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Therefore, Chapter 6 examines the prospects and problems associated with developing post-commercialization monitoring programs to detect and measure such effects. The potential environmental impacts of future products of genetic engineering may differ from those of the engineered crops that have recently been commercialized.
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2000) that ecological effects of agroecosystems compound to exert simplifying and destabilizing effects on neighboring ecosystems.
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1999, Gunderson 2000~. The committee cannot presently judge whether extensive commercialization of transgenics and other crops bearing novel traits will significantly perturb agroecosystems or neighboring ecosystems because of major gaps in our knowledge of these systems.
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In experiments on temperate North American grasslands, nitrogen enrichment caused species loss, and grassland plant communities that had lost species were much less resilient to rainfall and climate variation than more diverse communities that were not nitrogen-enriched (Tilman and Downing 1994, Tilman 1996~. Nitrogen deposition also reduces soil quality and fertility in surrounding ecosystems and causes freshwater acidification and coastal zone eutrophication (Tefferies and Maron 1997, Vitousek et al.
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Nutrient overenrichment from human activities is one of the major stresses affecting coastal ecosystems. There is increasing concern that in many areas of the world an oversupply of nutrients from multiple sources is having pervasive ecological effects on shallow coastal and estuarine areas.
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1996~. In addition to outflows of abiotic resources, agricultural activities often support increases in populations of organisms that then enter surrounding ecosystems, where they can exert a wide variety of effects (Carroll 1990~.
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Finding 1.1: There is substantial evidence that ecological effects of agroecosystems compound to exert simplifying and destabilizing effects on neighboring ecosystems. These effects are potentially of concern because they appear to weaken or destroy the neighboring ecosystems' capacity for resilience that is, an ecosystem's ability to maintain a certain state despite disturbance.
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The biological novelty introduced to agricultural systems by these varied activities can result from very small to very large changes in genetic information relative to preexisting organisms. The general degree of change in genetic information can be measured along two axes: the number of genetic changes and the taxonomic or phylogenetic distance between the source and the recipient of the new genetic information.
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From page 29... ...
Some participants in the debate over genetically engineered crops compare them to the products of conventional breeding because of the small number of genetic changes involved and have concluded that the need for oversight is minimal. Others compare genetically engineered crops to the introduction of new species because the new genetic information often originates from taxonomically distant species.
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In addition to attempts at explaining risk based on the number of introduced genes, studies have examined whether there is a relationship between the taxonomic or phylogenetic distance between the gene donor and recipient and the level of environmental risk. If level of risk increases with the phylogenetic distance between organisms exchanging genes, we might expect to find that documented cases of natural interkingdom horizontal gene transfer (the nonsexual transfer of the genetic material from one organism into the genome of another)
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4. Introduction of biological novelty can have unintended and unpredicted effects on the recipient community and ecosystem.
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5. There is no strict dichotomy between environmental risk associated with releases of conventionally bred crop cultivars and introduction of new species.
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In this regard the committee's findings support those of other scientists who have examined this problem of predicting risk and concluded that risk assessment cannot depend on general characteristics such as the amount of new genetic information introduced but must focus on the ecology of the specific introduced organism (or both the donor and recipient in the case of transgenic organisms) and the characteristics of the accessible environment into which the organism will be released (e.g., NRC 1987, Tiedje et al.1989, Scientists Working Group on Biosafety 1998~.
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small and large genetic changes have had substantial environmental consequences; b) the consequences of biological novelty depend strongly on the specific environment, including the genomic, physical, and biological environments into which they are introduced; c)
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As discussed earlier, the genetic basis for an altered crop trait can simply involve a single gene or can be complex, involving multiple, potentially interacting genes. Simply inherited traits are generally easy for plant breeders to manipulate because they usually show dominant or recessive phenotypes and produce simple ratios of progeny with and without the trait in segregating crosses.
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. Thus, knowledge of each gene is necessary but not sufficient to predict the final plant traits in a specific environment (Lewontin 2000~.
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For sexually reproducing species, simply inherited or single gene traits are usually incorporated into existing elite cultivars by the process of backcrossing. Backcrossing is conducted by crossing the elite cultivar with a donor (source of the single gene)
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1998~. One example of flower color variation in petunias results from a phenomenon called gene silencing, which occurred as a consequence of a duplicated gene sequence (Quideng and Jorgensen 1998~.
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to the elite parent in the case of simple traits or by selection of the best phenotypes in the case of complex traits. In this way, genes encoding the valuable trait are recovered in the nearly homogeneous elite genetic background.
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These techniques provide the opportunity to introduce novel and sometimes useful genetic traits. Most breeding programs make relatively little use of such potentially valuable genetic materials.
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1986; see also "Environmental Impacts of the Deliberate Introduction of Biological Novelty" above)
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tumefaciens containing genetically engineered T-DNAs (Birch 1997~. In the case of Arabidopsis, a model flowering plant used for basic research, developing flower buds can simply be soaked in liquid containing the bacteria in order for germ cells to become transformed with the T-DNA.
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1995~. Multiple transgene insertions and complex insertions at single loci are highly correlated with transgene silencing (see BOX 1.3)
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1999~. Although these genetically engineered recombination systems require additional steps for creating a transgenic trait, they are useful for removing selectable marker genes that are required to propagate a transgene in a bacterial and plant host cell.
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Consequently, a genetically engineered trait is usually transferred by sexual crossing followed by six or more generations of backcrossing into a more useful genetic background. This requirement has many of the same advantages and disadvantages of mutation breeding with conventional crops, as there is a certain amount of genetic drag associated with any nonelite genetic background.
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From page 48... ...
The line between conventional crop breeding and the creation of transgenic crops has never been perfectly clear, but the distinction between the two approaches is likely to blur even further. The genetic engineering process, per se, presents no new categories of risk compared to conventional breeding, although this technology could introduce specific traits or combinations of traits that pose unique risks.
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From page 49... ...
Finding 1.6: The transgenic process presents no new categories of risk compared to conventional methods of crop improvement, but specific traits introduced by both approaches can pose unique risks. Finding 1.7: Screening of all crops with added genetic variation must be conducted over a number of years and locations because undesirable economic and ecological traits may only be produced under specific environmental conditions.
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, APHIS argues that it is not treating transgenic organisms differently than so-called established plant pests or naturally occurring organisms, which may be plant pests. For example, APHIS regulates the movement and release of geographically separated populations of known plant pests because a new geographic population may have genetic characteristics absent in the recipient geographic population, which could increase the plant pest risk in the recipient population.
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From page 51... ...
They also provided a more formal process for applicants to petition the agency for nonregulated status of an engineered plant based on genetic and ecological knowledge of that plant (APHIS 1993~. A detailed analysis of APHIS oversight of genetically engineered plants is the focus of Chapters 3, 4, and 5.
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