The terminology used to describe various methods of genetic modification can have different meanings to different readers and can be interpreted in many ways. For the purposes of this report, the committee agreed upon a set of operational definitions for specific terms used to describe methods of genetic modification.
Although in popular parlance the term genetically modified (GM) often is used interchangeably with genetically engineered (GE) and biotechnology, in this report genetic modification refers to a range of methods used to alter the genetic composition of a plant or animal, including traditional hybridization and breeding. Genetic engineering is one type of genetic modification that involves making an intentional targeted change in a plant or animal gene sequence to effect a specific result (see Figure 1-1) through the use of recombinant deoxyribonucleic acid (rDNA) technology. Biotechnology refers to methods (including genetic engineering) other than conventional breeding used to produce new plants, animals, and microbes. Conventional breeding is used to describe traditional methods of breeding, or crossing, plants, animals, or microbes with certain desired characteristics for the purpose of generating offspring that express those characteristics.
As exemplified by Mendel’s research, conventional breeding by crossing has been conducted for centuries to produce genetic modifications in crop plants and farm animals. Even his early experiments, while relatively simple from today’s perspective, yielded unexpected results (Mendel, 1866). The concept of dominant inheritance stems from Mendel’s unexpected finding that in a cross of white- and red-flowered plants in which the parents were homozygous, the first generation was uniform (F1) but none of the offspring showed an intermediate color, and the second generation (F2) produced three times more red- than white-flowered offspring. This result helped illustrate the distinction between phenotype (physical characteristics) and genotype (genetic pattern).
Plants and animals can be genetically modified in a variety of ways, each requiring some level of human intervention. Traditional methods include selection and crossbreeding, while more contemporary techniques include embryo rescue, cell fusion, somaclonal variation, mutation breeding, and cell selection. Genetic engineering, or rDNA modification, is achieved through different techniques leading to specifically designated genetic changes. There also are methods of genetic manipulation, different from rDNA technology, that use viral vectors to introduce foreign DNA into host cells.
All methods of genetic modification hold the potential, either intentionally or unintentionally, to alter levels of primary metabolites (such as proteins, lipids,