. "2. Potential Environmental and Human Health Implications of Pest-Protected Plants." Genetically Modified Pest-Protected Plants: Science and Regulation. Washington, DC: The National Academies Press, 2000.
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GENETICALLY MODIFIED PEST-PROTECTED PLANTS: SCIENCE AND REGULATION
BOX 2.1
Summary of Genetic Basis of Resistance Traits That Have Been Bredinto Cultivated Plants Using Conventional and Transgenic Techniques
Conventionally bred plants only
Polygenic traits2 (controlled by several interacting genes, usually selected without knowledge of which genes are involved)
Both Conventionally bred and transgenic plants
Single-gene traits2 from the same species or a related species
Several single-gene traits that are not genetically linked and are therefore inherited independently
Several single-gene traits that are physically linked and inherited as a unit; occasionally possible with conventional breeding, as when a chromosome segment bearing more than one resistance gene is transferred to the cultivar usually accompanied by extraneous DNA; transgenic methods allow several single-gene traits to be tightly linked without extraneous DNA
Single-gene traits expressed only in particular tissues or at particular developmental stages because of specific promoters; occasionally possible with conventional breeding, but more flexible and precise with transgenic methods
Transgenic plants only
Single-gene traits found in the same species or a related species and modified by changes in the nucleotide sequence of the structural gene or the promoter to improve the plant's phenotypic characteristics
Single-gene traits obtained from unrelated organisms (such as viruses, bacteria, insects, vertebrates, and other plants); sometimes modified by a change in the nucleotide sequence of the structural gene or the promoter to improve the plant's phenotypic characteristics
Single-gene traits that can be induced by a chemical spray or by specific environmental conditions (such as threshold temperature), based on the action of specific promoters; (these traits may also occur naturally in nontransgenic plants, such as those with systemic acquired resistance, but have rarely been selected intentionally by conventional breeding)
The committee recognizes that the magnitude of the risk varies on a product by product basis. The committee also agrees with points 1 and 2 in the sense that the potential hazards and risks associated with the organisms produced by conventional and transgenic methods fall into the
2
A molecular technique known as marker-assisted selection can speed the identification of polygenic or single-gene traits in the plant 's own genome, and rapid advances in genomics are expected to speed the identification of additional single-gene resistance traits in plants and other organisms.
