single base changes, insertions and deletions). The typical variation we see in the traits of organisms generally involves naturally occurring mutations. Natural mutations and mutations induced by chemicals and radiation have been used to produce many commonly used cultivars. In general, few genes are modified and most of the genome is unaffected. Most mutations are from an active form to a less active form and would pose a problem only when the active form is needed to remove an antinutritional, allergenic, or toxic constituent.
Somaclonal variation is considered to be a form of induced mutagenesis occurring during the tissue culture process. The reason for interest in somaclonal variation is that it increases the genetic variation in plants regenerated from tissue culture; one of the general procedures used to develop transgenic plants. Its potential for unfamiliar health effects would be similar to that of mutagenesis.
Somatic-cell fusion has the potential to combine whole genomes from genotypes of widely divergent genera. However, it is rare for a somaticfusion hybrid from widely divergent genera to be directly commercialized. More likely, the genes contributed from one genus would be reduced with another breeding technique or genetic manipulation (such as backcrossing). According to the rationale described above for sexual hybridization, somatic-cell fusion involving cells from the same species (intraspecific hybrids) would have a lower potential for adverse health effects than interspecific hybrids, which would have a lower potential than intergeneric hybrids.
Introduction of transgenes into plants typically involves random integration of DNA into the nuclear genome and the use of tissue culture, which can lead to somaclonal variation. If integration of a transgene occurs within or near a gene, there is a potential for unintended consequences. Disruption of a gene can lead to its down-regulation or inactivation. If the gene is essential, viable plants will not be recovered after the transformation or transgene introduction. If the gene is not essential for growth and development, viable transgenic plants will be recovered, but they might have unexpected traits.
Introduction of a transgene can also result in activation or up-