Part 1: Basic Principles
Rakesh S. Chandran, Ph.D.
WVU Extension Service
This article was published in the November 2000 issue of West Virginia Farm Bureau News.
For ancient man, most naturally occurring phenomena were a mystery. Today, we have answers to some of the most complicated questions.
The concept of genetic engineering, however, is widely different from that of other scientific advances because it deals with the underlying mechanisms of life itself. It is essential to thoroughly understand this science to make sound judgments about it.
A series of three articles will cover basic principles, pros and cons, and future directions of this technology. Although genetic engineering has an impact on almost all aspects of life, these articles will focus primarily on genetically engineered crops.
First, what is a genetically engineered crop? We know that genes determine the physical characteristics of plants and animals. We also know that genes reside in cells, the fundamental units of all living organisms. Genes are actually sections of genetic material known as DNA (deoxyribonucleic acid), which has coded information that eventually determines an organism’s physical traits.
How is this information coded in a gene or DNA? DNA is essentially composed of long chains of units called bases, just like links of a long chain. although there are millions of these links or bases in a single DNA strand, they are actually made up of four kinds of bases-A, T, G, c (comparable to the 26 letters of the English alphabet). The arrangement of a vast number of these four bases in a DNA molecule can be referred to as the genetic code.
The bases are arranged in a predetermined sequence that makes up the genetic code for producing a variety of proteins. Three of these bases form a code for a certain biochemical called an amino acid. Twenty amino acids, which are the building blocks of proteins, can be produced. The amino acid produced depends on the bases’ sequence on the gene. The sequence of amino acids in the chain determines the nature and characteristics of these proteins. The proteins eventually determine the physical traits of the particular organism. Therefore, a slight rearrangement of the bases in a DNA molecule may alter the organism’s traits or characteristics.
Throughout evolution, natural selection has caused organisms to adapt to their surroundings. These adaptations originated from a rearrangement or mutation of the bases (genetic code), often by natural causes. This is a very slow process. Through reproduction, the parents transmit genes to the offspring. Understanding this enabled us to use classical breeding techniques to improve corps and domestic animals. Classical breeding involves humans introducing new genetic material to the offspring. However, organisms are capable of reproducing only within species or between very closely related species. Therefore, classical breeding was limited to generating hybrids within a given species or between closely related ones.
Now, we can introduce genes from distantly related species into an organism’s DNA. Genetically engineered crops have foreign genes. The gene introduced into the plant may have originally belonged to a totally different plant, a microbe, or even an insect or an animal.
For example, Bt corn, a genetically modified crop, contains genes belonging to a bacterium called Baccilus thurengiensis. By nature, this bacterium is capable of infesting the European corn borer through its chemical secretions. After the bacterial genes are introduced into Bt corn, the corn can produce Baccilus thurengiensis chemicals to infest the insect. When a European corn borer larva feeds on Bt corn, it ingests some of these chemicals and dies. The corn thus becomes resistant to this serious pest.
As a science, biotechnology is still in its infancy. Future research will give us a better picture of its long-term effects. It is premature to rule out the usefulness of this technology or to embrace it entirely. Part 2 of this series will discuss some of the benefits and risks of genetically engineered crops.