Genetically Engineered Crops—
Agricultural Biotechnology Concepts
and Definitions
"For thousands of years, genes have been manipulated empirically by
plant and animal breeders who monitor their effects on specific characteristics
or traits of the organism to improve productivity, quality, or performance.
A basic understanding of how traits are transmitted was formed by Gregor
Mendel in the 19th century. His experiments and concepts showed that traits
were controlled by units of heredity called genes. Extensions of his work
led to the formation of applied genetics and breeding programs. The physical
and chemical nature of genes remained unknown until the 1950s when James
Watson and Francis Crick discovered that genes consist of a chemical known
as DNA (Deoxyribonucleic acid). DNA contains the information to control
the synthesis of enzymes and other proteins that perform the basic metabolic
processes of all cells. Each gene is a specific DNA sequence, and more
than 100,000 different genes are found in a higher plant or animal species.
This total set of genes for an organism (referred to as the nuclear genome)
is organized into chromosomes within the cell nucleus. The process by
which a multicellular organism develops from a single cell through an
embryo stage into an adult is ultimately controlled in the genetic information
of the cell and by interaction of genes and gene products with environmental
factors." —Vodkin, L.O. "Jumping Genes that Control Plant
Traits," in Research for Tomorrow, 1986 Yearbook of Agriculture.
USDA, Washington, DC, 1987.
Biotechnology is broadly defined as
the use of biological processes of microbes, and of plants or animal cells
for the benefit of humans.
Bt crops are genetically engineered to carry
the gene from the soil bacterium Bacillus thuringiensis. The bacteria
produces a protein that is toxic when ingested by certain Lepidopteran
insects. Crops containing the Bt gene are able to produce this toxin,
thereby providing protection throughout the entire plant.
Bt cotton is genetically
engineered to control tobacco budworms, bollworms, and pink bollworms.
Bt corn is genetically engineered to provide protection against
the European corn borer.
Cell is the smallest structural unit of living
organisms that is able to grow and reproduce independently.
Elasticity refers to the case where
one economic variable causes a change in another (e.g. price and quantity
demanded). In general, elasticity measures the responsiveness of one economic
variable to a change in another. It is unit free and always expressed
in percentage terms.
Genetic engineering, very broadly, is a technique used to alter
or move genetic material (genes) of living cells. Narrower definitions
are used by agencies that regulate genetically modified organisms (GMO's).
In the United States, under guidelines issued by USDA's Animal and Plant
Health Inspection Service, genetic engineering is defined as the genetic
modification of organisms by recombinant DNA techniques (7CFR340: 340.1).
Definitions used in Europe are somewhat broader.
Gene stacking involves combining traits (such as herbicide tolerance
and insect resistance) in seed.
Herbicide-tolerant
crops were developed to survive certain herbicides that previously would
have destroyed the crop along with the targeted weeds, and allow farmers
to use them as postemergent herbicides, providing an effective weed control.
The most common herbicide-tolerant crops (cotton, corn, soybeans, and
canola) are Roundup Ready (RR) crops resistant to glyphosate, a herbicide
effective on many species of grasses, broadleaf weeds, and sedges. Other
genetically modified herbicide-tolerant crops include Liberty Link (LL)
corn resistant to glufosinate-ammonium, and BXN cotton resistant to bromoxynil.
Plant breeding is use of techniques involving crossing plants
to produce varieties with particular characteristics (traits), which are
carried in the genes of the plants and passed on to future plant generations.
Transgenic plants result from the insertion of genetic material
from another organism so that the plant will exhibit a desired trait.
Recombinant DNA techniques (DNA formed by combining segments of DNA from
different organisms) are usually used.
For additional definitions visit the Food
and Agricultural Organization's biotechnology glossary
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