1. An Introduction to Biotechnology

Biotechnology is a word used to describe the process of using living organisms (such as plants, animals, or microbes) or any part of these organisms to create new or improved products. The term is most often associated with methods and techniques developed during the past 20 years that make use of the cells and biological molecules of living organisms. But biotechnology, in some ways, is not very new at all. For six thousand years, we have been using microbes to make useful products such as bread, yogurt, and cheese. Also, for thousands of years, people have altered the genetic makeup of plants and animals to make them more useful. For example, growers have improved the characteristics of crops by planting seeds selected from the biggest and best individual plants. Through this selection process, desirable characteristics have been promoted. Plants have been cultivated and animals have been domesticated, changing them from their wild beginnings to forms more useful to humans. While this process is slow, it has been quite successful.

Early Breeding Programs

Because people involved in agriculture could clearly see the benefits of improving plants and animals, scientists developed a keen interest in understanding how organisms inherit certain characteristics. Plant breeding as a science began in the 19th century with the discovery of how plant traits are inherited. Gregor Mendel discovered that the characteristics of plants and animals are determined by genes, which are a fundamental part of the nucleus of each cell in an organism, and that the genes carry certain traits from each parent to the offspring when organisms reproduce. Of course, not all plants and animals of a given species are identical; some have different traits that make them more desirable for agricultural production--for example, higher yield or greater resistance to drought. Plant breeders select plants with desirable traits after the exchange of genes by cross-fertilization between two parents. They then ensure that these traits will be passed on to future generations, thus creating a new variety of the plant. (A variety is a subgroup within a species and has distinctive traits that are different from other members of the species.)

People have utilized the diversity of plants in nature as sources of food and fiber for thousands of years. We have changed and will continue to change these plants to better meet human needs.

Most of the early breeding programs were based on the collection of different specimens of the same species of plant from throughout the world. This approach allowed breeders to obtain as much of the genetic variation as was available within the species worldwide. Then through conventional breeding techniques they tried to utilize desirable characteristics to improve the domesticated varieties of those species.

This process is the basis for the development of essentially all varieties of plants and animals used in agriculture today. However, it is slow, commonly requiring 10 years before a new variety is ready to be released. But the biggest problem is that a desirable characteristic being sought to improve a given species may not be found among any of the plants or animals of that species in the world. Further improvement by conventional breeding can thus reach a dead end for that desired trait. For example, if resistance to a particular insect is needed in a given crop species and no such resistance is found in any plant of that species in the world, then protection of that crop may be dependent upon insecticides.

With new techniques, however, the path to genetic improvement need not end that soon. If resistance to the insect is found within a different species (animal, plant, or microbe), modern methods make it possible to transfer that resistance to the plant species of interest. The same methods could be used to increase yield, improve cold hardiness, or add any desirable characteristic. The source for genetic resources is expanded to include all living species, making the possibility of improvements virtually unlimited. Modern techniques fall into three categories: cross-breeding between species, cell fusion, and genetic engineering.

Breeding Between Species (Interspecific Hybridization)

The reproductive process through which genetic material is transferred between individuals of a species does not normally work between species. The desire to improve certain crops, however, has led plant breeders to develop processes for interspecific (between-species) hybridization to transfer genes from one plant to another plant of a related species. This transfer has been accomplished during the last 80 years only through the discovery of efficient ways to circumvent the natural barriers to the exchange of genetic information between species.

The processes for interspecific gene transfers are usually laborious, time consuming, and quite often unsuccessful. There are many steps in the process of developing a hybrid plant, and each step is a possible point for failure, either through death or sterility of the plant. Even when a hybrid plant is created, there is a possibility that undesirable traits that affect crop quality, yield, or adaptation to stress may be transferred along with the desirable trait.

For thousands of years, corn plants have been selected for their desirable traits. Some of the various types of corn include (left) an old species of popcorn, an old type of corn now used for ornamental corn, and a red ceremonial corn; (right) modern pod corn, modern yellow corn, and modern white corn.

Even with all of these problems, interspecific hybridization has been responsible for many improvements in the tolerance of crops to physical stresses (such as cold), resistance to diseases and insects, and increased yield potential for certain crops. The process has even made possible the development of a new grain crop, triticale, from the hybridization of wheat and rye.

Cell Fusion

Microbiologists and breeders have been looking for alternate means to transfer genes. Such exchange of genes depends on the scientist's ability to regenerate a plant from tissues or organs (leaves, stems, or even clumps of cells in culture). Much effort has been devoted to cell fusion, a process for combining two cells of the same or different species in the presence of certain chemicals or electrical current. In addition to the problem of regenerating a complete plant from the resulting cell, it is often difficult to achieve a stable hybrid (one that will retain the same characteristics through many generations) because of incompatibility between the parent species. As with interspecific hybridization, many genes are transferred during the cell fusion process, and thus unwanted traits may be transferred with the desirable ones. Further crosses may be necessary to obtain plants with the desired combination of parental traits.

Genetic Engineering

Another method for transferring genes is to move the DNA directly. (DNA is the molecule within the cell that carries genetic information.) Direct combining of DNA is called genetic engineering. New techniques make it possible to use genes from totally unrelated organisms. First, scientists identify genes that control specific functions or characteristics--for example, improved insect resistance or production of enzymes for the degradation of a certain herbicide. Then they move these genes into the host plant. One of the advantages of this system is the ability to move just the trait of interest without carrying along any undesirable genes.

With genetic engineering, the time from discovery to incorporation of a desirable trait into a host organism will usually be shorter than with the use of classical breeding techniques to produce new varieties.

Genetic engineering may help crop producers reduce dependence on pesticides by affecting the plant's resistance or tolerance to pests in the field. It can also affect production efficiency and profitability by improving the climatic adaptation of the plant (for example, its tolerance to cold or drought) and by enhancing the postharvest storability of the product.