and regulated should allow design of resistant plants in which the active compound is expressed in defined locations within the plant. New Bt endotoxins with different specificities or targets are on the horizon, as are a variety of novel or pathogen-derived resistance strategies that have high efficiency and specificity.

A major goal of future development of pest-protected plants should be to decrease the potential for ecological and health risks that may be posed by some types of pest-protected plants (section 2.2.1). This work could include using marker-assisted breeding to avoid selecting varieties with inadvertently high levels of potential toxins and limiting expression of transgenes that have potential adverse nontarget effects to nonedible plant tissues. Development of strategies that enhance the effective life span, or durability, of transgenic pest-protection mechanisms is also of vital importance.

2.4 POTENTIAL HEALTH EFFECTS OF DIVERSE GENE PRODUCTS AND BREEDING METHODS

Sections 2.1 and 2.2 discussed standard risk-assessment terminology for GMPP plants and the 1987 NAS principles. One of the conclusions from those sections was that quantitative risk would vary case by case and depend on the gene product (hazard), its potency (hazard severity and dose-response relationship), and magnitude of exposure levels (exposure assessment). The following two subsections discuss the potential of various gene products (discussed in section 2.4.1) to cause adverse health effects and the potential of various genetic modification techniques (discussed in section 2.4.2) to cause indirect effects regardless of the intended gene product.

2.4.1 Health Effects Associated with Different Types of Gene Products

Different types of transgenic pest-protected plants that might be developed have the potential to cause adverse health effects. The degree of risk is related to the chance that potentially hazardous toxic or allergenic compounds are produced and to the magnitude of exposure of such compounds. The chance that hazardous compounds will be produced by either intended or unintended modifications is related largely to the specific type of transgene used.



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