proportion of oleic acid. However, the conventionally bred high oleic soybeans can be unstable—depending on environmental conditions, their fatty acid content may vary—while the GE high oleic soybean remain more stable (DHHS, 1996).

Other rDNA examples exist where foreign DNA is not necessarily present. The first GE food product approved for human consumption in the United States, the Flavr Savr tomato, was engineered with an inverted tomato gene (CFSAN, 1994), along with bacterial genes transferred to facilitate selection of the modified plant. In the absence of foreign DNA or genes from another species, an argument may be made that a GE plant is not transgenic and not unnatural if only native DNA is transferred. One could readily transfer genetic material from one tomato variety to another, or rice to rice, or soybean to soybean without any other contributing source of DNA.

A recent report of a similar case involved a coffee variety being engineered to produce less caffeine as an alternative to current industrial methods of decaffeination (Ogita et al., 2003), which may use benzene or other organic solvents for extraction. Using rDNA methods, Ogita and colleagues (2003) were able to transform coffee and observe a 70 percent reduction in caffeine in leaves. Because their intent was to interfere with the natural caffeine biosynthetic pathway in the coffee plant, the objective also could have been pursued with an induced mutation breeding program. However, the rDNA method was preferred because it was more precise and predictable, as well as less likely to induce deleterious mutations unrelated to caffeine.

Genetic recombination occurs in both nature and in human-mediated genetic engineering of plants, animals, and microorganisms (see Box 3-4). This section examines recombination as it occurs in nature and as it occurs with genetic engineering, with particular reference to differences between the two processes. 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).

Homologous recombination occurs when DNA strands with similar or homologous base sequences spontaneously recombine with one another. Such juxtaposed sequences do not have to be identical for recombination to occur, but the incidence of recombination between nonidentical sequences diminishes in proportion to the degree of sequence dissimilarity (Lewin, 1985).

Chiasmata are chromosomal crossover events, visible under the microscope, in which whole segments of chromosomes are exchanged. These exchanges often