Genetic Engineering in Agriculture
Among the millions of species that inhabit the planet, only twenty species provide ninety percent of the human food supply (Montgomery 2000). Since the introduction of genetic engineering, however, livestock and crops have a more productive future. Transfer of engineered genes from organism to organism occurs through hybridization, conjugation, and transformation in microorganisms. By the substitution of genes into agricultural species, biodiversity can flourish to improve social and economic development. Although methods of gene and DNA implantation quickly develop advanced products, even precise genetic alterations do not ensure that the environment will remain balanced or that changes in the genome will not occur. With careful design and a good understanding of transgenic organisms, minimal ecological and social risks will occur with the development of genetically engineered organisms.
To improve methods of plant breeding, farmers turn to the hybridization of genes. New genes from wild species are transferred into cultivated varieties of similar crops to attain desired traits. Specific properties such as disease resistance, stress tolerance, and nutritional qualities are advantageous to the farmer because more time is spent on cultivation rather than outside interferences. However, crossbreeding results in mass amounts of genes transferring to the plant recipient, only a few of which are desired. Thus, only sexually compatible species of the crop can be used to breed (Horsch 1993). Farmers using crossbreeding and hybridizing methods are able to attain improved products, but could cause great damage to the genome in the transfer of unknown, undesired genes (Geweke 1999).
In more recent biotechnology, breeders are turning to genetic transformation as a more precise method of genetic engineering. Instead of transferring large blocks of genes from donor plant to recipient, small isolated blocks of genes are put into the plant chromosome through biolistics, vectors, or protoplast transformation (Horsch 1993). Biolistics is a technique that shoots the gene block into the potential host cell. In order for the process to succeed, the microscopic particles and DNA must enter the cell nuclei and combine with the plant chromosome. Biolistics is commonly used but has a slight failure risk since the breeder has little control over the destination of the gene block (Mooney & Bernardi 1990). Bacteria or viruses can also carry the gene blocks into a new cell. Common vectors in gene transfer between plants are Agrobacterium tumefaciens and Agrobacterium rhizogenes. In the soil, the bacteria will infect the plants with their own plasmid, transferring the desired gene that was placed in the bacteria's DNA. Vector gene transfer is a preferred method of transformation since this modification already occurs naturally in the environment (Rudolph & McIntire 1996). Last is protoplast...