Safety of Genetically Engineered Foods Approaches to Assessing Unintended Health Effects (2004) / Chapter Skim
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3 Unintended Effects from Breeding
3 Unintended Effects from Breeding
Pages 39-72
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From page 39... ...
However, through the breeder's selection process, the genetic lines that express undesirable characteristics are eliminated from further consideration, and only the best lines -- those that express desirable characteristics with no additional undesirable agronomic characteristics, such as increased disease susceptibility or poor grain quality -- are maintained for possible commercial release. Although plants and animals produced from conventional breeding methods are routinely evaluated for changes in productivity, reproductive efficiency, reactions to disease, and quality characteristics, they are not routinely evaluated for unintended effects at the molecular level.
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From page 40... ...
PLANT BREEDING Conventional Plant Breeding Conventional plant production occasionally generates foods with undesirable traits, some of which are potentially hazardous to human health. Most crops naturally produce allergens, toxins, or other antinutritional substances (see Chapter 5)
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From page 41... ...
. Unintended Effects of Conventional Plant Breeding Naturally Occurring Toxins All foods, whether or not they are genetically engineered, carry potentially hazardous substances or pathogenic microbes and must be properly and prudently assessed to ensure a reasonable degree of safety.
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From page 42... ...
Certain potato lines have been found to express greater disease- or pest-resistance, and they have been selected as superior, not always with favorable or intended results. The most notorious such selection was the Lenape potato, which was developed using conventional breeding methods (Akeley et al., 1968)
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From page 43... ...
. This singular result shows that non-genetic engineering breeding methods can have unintended effects and generate potentially hazardous new products.
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From page 44... ...
. Moreover, celery cultivars produced using conventional breeding methods -- intended to enhance insect-resistance and aesthetic appeal to consumers through in creased production of psoralen -- have been associated with cases of der matitis among grocery workers, as well as further cases of photosensitivity among farm workers handling these plants (Ames and Gold, 1999)
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From page 45... ...
In spite of these intrusive methods, induced mutagenesis is considered a conventional breeding technique. Food derived from mutation breeding varieties is widely used and accepted.
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From page 46... ...
Evaluation of GE food products for other countries is described above, in the section Conventional Plant Breeding. Genetic engineering methods are considered by some to be more precise than conventional breeding methods because only known and precisely characterized genes are transferred.
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From page 47... ...
lists more than 10,000 field trials with GE plants that were conducted between 1986 and 1999. Most of these authorized trials were conducted on plants genetically engineered by public universities and government research institutions, not for commercial release but to test the plants for unexpected or unintended results (see OECD, 2000)
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From page 48... ...
. This phenomenon occasionally occurs with conventional breeding, so its occurrence in a GE petunia does not indicate a unique GE phenomenon.
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From page 49... ...
For example, the comparison between Arabidopsis and a herbicide-tolerant variety is misleading because the comparator was a mutant variety of uncertain genetic composition. In addition, as discussed earlier, undesirable, unexpected, and unintended traits are noted in conventional breeding lines of commercial crop species on rare occasions, and these lines are consequently discarded.
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From page 50... ...
Unintended Effects from Conventional Animal Breeding Double-Muscling In beef cattle some non-GE mutant animals show the presence of extraordinary quantities of muscle. The muscular hypertrophy, referred to as double-muscling, is a heritable trait that primarily results from an increase in the number of muscle fibers or cells rather than an increase in the size of individual muscle fibers.
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From page 51... ...
The overlay of biotechnology and conventional breeding will likely occur in phases that involve broad genetic maps with informative microsatellite markers and evolutionarily conserved gene markers; use of microsatellite markers to identify quantitative trait loci (QTL) of commercially important traits, based on knowledge of complex pedigrees or crosses between phenotypically and genetically divergent breeds or strains; identification of specific trait genes and/or use of conserved markers to identify candidate genes based on their position in gene
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From page 52... ...
Genetic Engineering As with plant breeding, animal breeding programs and the production of transgenic farm animals can result in unintended effects. Most, but probably not all, gene-based modifications of animals for food production or therapeutic claims fall under the FDA Center for Veterinary Medicine regulations of new animal drugs.
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From page 53... ...
. This variability contributes enormously to any effort to assess the unintended effects of genetic modification and to evaluate whether any unintended effect that occurs is possibly a cause for a health concern in humans.
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The following is a brief overview of unintended effects associated with cloning technology. Cloning by nuclear transfer from embryonic blastomeres (Willadsen, 1989; Willadsen and Polge, 1981)
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MECHANISMS BY WHICH UNINTENDED EFFECTS IN GENETICALLY ENGINEERED ORGANISMS ARISE Unintended effects may arise from one or more of several mechanisms, which can be either systemic or individual. Systemic effects are those likely to appear in all or almost all transgenic plants, animals, or microbes transformed using the same genetic engineering method and DNA construct.
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From page 56... ...
list several examples of documented unexpected effects in transgenic plants. Genetic Instability A frequently stated concern about the use of rDNA technology is that transgenic organisms may be genetically unstable.
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From page 57... ...
Both conventional breeding via induced mutagenesis and rDNA transfer of genes from other soybean varieties have been used to generate new soybeans with a higher
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From page 58... ...
Natural recombination occurs in several ways, typically divided between homologous and nonhomologous recombination events. Genetic recombination events that occur specifically in animals are summarized in Chapter 2 and are discussed in detail in the report Animal Biotechnology: Science-Based Concerns (NRC, 2002)
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From page 59... ...
The potato is another example of a common food developed from a combination of genes from different species. Several popular potato variet ies were developed using conventional breeding methods to bring useful genes from foreign species into the common potato variety S
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From page 60... ...
Such latitude allows the possibility of insertion into a functional gene, thus inactivating it, in contrast to homologous recombination where the DNA sequence at the locus of insertion is known, that is, identical or near identical with the insertional DNA with the recombined gene generally retaining functionality. This factor makes nonhomologous recombination less attractive to breeders than homologous recombination because nonhomologous recombination events will have to be more stringently screened to identify and eliminate inserts into and possible inactivation of nontarget genes.
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From page 61... ...
If genetic instability were more common or synchronized, such that it were noticeable, the breeder would not be able to obtain certification for the new variety due to failure to meet the genetic stability requirement. Genetic instability is observed from time to time, both in conventional breeding and in genetic engineering.
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From page 62... ...
THE GENETIC MANIPULATION CONTINUUM Overview Predicting the likelihood of unintended hazards from compositional changes associated with genetic modifications does not fit a simple dichotomy comparing genetic engineering with non-genetic engineering breeding. This is because there are many mechanisms shared in common by both GE and non-GE methods, and also because there are techniques that slightly overlap each other.
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From page 63... ...
. Analysis of the Continuum As noted earlier in this chapter, unintentional changes are possible with all conventional and biotechnological breeding methods for genetic modification.
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From page 64... ...
64 likely a More methods the only of fects, None ef fect. ef fects.
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From page 65... ...
It is unlikely that all methods of either genetic engineering, genetic modification, or conventional breeding will have equal probability of resulting in unintended changes. Therefore, it is the final product of a given modification, rather than the modification method or process, that is more likely to result in an unintended adverse effect.
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From page 66... ...
All forms of genetic modification, conventional and modern, may potentially lead to unintended changes in composition, some of which may have adverse health effects. The range of biotechnology methods, including genetic engineering, makes it possible to alter, add, or remove genes from conventional food organisms.
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From page 67... ...
Conventional breeding methods have also provided new crop varieties with enhanced herbicide tolerance, pest resistance, and other non-nutrient characteristics, as well as enhanced nutritional profiles, posing potential risks from ingestion that are similar to genetic engineering. Similar comparative examples can be found in animal breeding and in microbial strains, in which conventional methods have produced new products with unintended hazards similar to those that may result as a consequence of the application of rDNA technology.
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From page 68... ...
1993. Linear furanocoumarins of three celery breeding lines: implications for integrated pest management.
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From page 69... ...
2001. Assessment of the food safety issues related to genetically modified foods.
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From page 70... ...
Reduced Fusarium ear rot and symptomless infection in kernel of maize genetically engineered for European corn borer resistance. Phyto pathology 87:10711077.
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From page 71... ...
2000. Safety Aspects of Genetically Modified Foods of Plant Origin.
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