Using Biotechnology to Modify Plants and Animals

Combining DNA from different existing organisms (plants, animals, insects, bacteria. etc.) results in modified organisms with a combination of traits from the parents. The sharing of DNA information takes place naturally through sexual reproduction and has been exploited in plant and animal breeding programs for many years.

However, sexual reproduction can occur only between individuals of the same species. A Holstein cow can be mated with a Hereford bull because the two animals are different breeds of the same species, cattle. But trying to mate a cow with a horse, a different species of animal, would not be successful.

What's new since 1972 is that scientists have been able to identify the specific DNA genes for many desirable traits and transfer only those genes, usually carried on a plasmid or virus, into another organism. This process is called genetic engineering and the transfer of DNA is accomplished using either direct injection or the Agrobacterium, electroporation, or particle gun transformation techniques. It provides a method to transfer DNA between any living cells (plant, animal, insect, bacterial, etc.). Virtually any desirable trait found in nature can, in principle, be transferred into any chosen organism. An organism modified by genetic engineering is called transgenic.

Products of Genetic Engineering

Specific applications of genetic engineering are abundant and increasing rapidly in number. Genetic engineering is being used in the production of pharmaceuticals, gene therapy, and the development of transgenic plants and animals.

Pharmaceuticals. Human drugs such as insulin for diabetics, growth hormone for individuals with pituitary dwarfism, and tissue plasminogen activator for heart attack victims, as well as animal drugs like the growth hormones, bovine or porcine somatotropin, are being produced by the fermentation of transgenic bacteria that have received the appropriate human, cow, or pig gene.

Gene Therapy. The first clinical gene therapy is underway to correct an enzyme deficiency called ADA in children. Bone marrow cells are removed, defective DNA in bone marrow cells is supplemented with a copy of normal DNA, and the repaired cells are then returned to the patient's body.

Transgenic Plants. Transgenic plants that are more tolerant of herbicides, resistant to insect or viral pests, or express modified versions of fruit or flowers have been grown and tested in outdoor test plots since 1987. The genes for these traits have been delivered to the plants from other unrelated plants, bacteria, or viruses by genetic engineering techniques.

Transgenic Animals, Presently, most transgenic animals are designed to assist researchers in the diagnosis and treatment of human diseases. Several companies have designed and are testing transgenic mammals that produce important pharmaceuticals in the animal's milk. Products such as insulin, growth hormone, and tissue plasminogen activator that are currently produced by fermentation of transgenic bacteria may soon be obtained by milking transgenic cows, sheep, or goats.

Using Biotechnology in Diagnostic Applications

Since each living creature is unique, each has a unique DNA recipe. Individuals within any given species, breed, or hybrid line can usually be identified by minor differences in their DNA sequences – as few as one difference in a million letters can be detected! Using the techniques of DNA fingerprinting and PCR (polymerase chain reaction) scientists can diagnose viral, bacterial, or fungal infections, distinguish between closely related individuals, or map the locations of specific genes along the vast length of the DNA molecules in the cells.

Identifying Organisms

By using RFLP technology (restriction fragment length polymorphism), DNA fingerprints can be generated. Any individual organism can be uniquely identified by its DNA fingerprint. Consequently, this fingerprint can be used to determine family relationships in paternity litigation, match organ donors with recipients in transplant programs, connect suspects with DNA evidence left at the scene of a crime (in the form of hair or body fluids), or serve as a pedigree for seed or livestock breeds.

Identifying Genes

One important aspect of genetic engineering projects is to identify the DNA gene that controls a particular trait. In the same way that a visitor might use the state, city, street, and house number to locate a friend's house, genetic engineers use genetic "maps" to locate genes. The genetic maps are generated by statistical analyses, PCR, RFLP, and DNA sequencing. Maps are being developed for humans, mice, swine, cattle, corn, wheat, and other plants or animals with commercial or research importance.

Diagnosing Infectious Diseases and Genetic Disorders Diagnosis of infectious diseases is a profound application of the new DNA technology. Tuberculosis, AIDS, papillomavirus, and many other infectious diseases, in addition to the inherited disorders like cystic fibrosis or sickle cell anemia, are diagnosed within hours by the PCR technique rather than days or weeks by traditional methods. The greatly increased sensitivity and speed of the PCR technique, as compared with traditional methods, allows earlier intervention and treatment. PCR assays will soon be available to diagnose diseases of crops and livestock.

Glossary

Agrobacterium – a natural bacterium that can be used to transfer DNA genes into broadleaf plants, such as tobacco, tomato, or soybean.

Chromosome – a cellular structure comprised of a long, folded DNA molecule and protein.

DNA – deoxyribonucleic acid, the substance within cells that carries the "recipe" for the organism and is inherited by offspring from parents.

DNA fingerprinting – cutting a DNA chromosome with restriction enzymes and separating the pieces by electrophoresis to generate a unique pattern, the "fingerprint" for each species, breed, hybrid, or individual, depending on which enzymes and probes are used.

Electrophoresis – a lab technique for determining DNA fragment sizes by separating them in a gel placed in an electric field.

Electroporation – using an electric shock to transfer DNA into the cells of an organism; one of several procedures called transformation.

Gene – a functional unit of DNA, one "word" in the DNA recipe.

Genetic code – the information contained in DNA molecules that scientists describe on the basis of a 4-letter alphabet (A, C, G, and T).

Genetic engineering – the process of transferring DNA from one organism into another that results in a genetic modification; the production of a transgenic organism.

Genetic map – the locations of specific genes along a chromosome marked with probes.

Genome – the entire DNA "recipe" for an organism, found in every cell of that organism.

Mutation – a change of one of the "letters" in the DNA "recipe" caused by chemicals, ultraviolet light, X-rays, or natural processes.

Particle gun – a gun that shoots DNA into the cells of an organism; the most versatile of a series of procedures called transformation.

PCR – polymerization chain reaction, which rapidly duplicates specific DNA molecules in response to temperature changes in a computer-controlled heater.

Plasmid – a small, circular DNA that is used to transfer genes from one organism into another.

Probe – a very short piece of DNA used to find a specific sequence of "letters" in a very long piece of DNA from a chromosome or genome.

Recombinant DNA – DNA formed by joining pieces of DNA from two or more organisms.

RFLP – restriction fragment length polymorphism, which describes the patterns of different (polymorphism) sizes of DNA (fragment length) that result from cutting with restriction enzymes (restriction). See DNA fingerprinting above.

Sequence – the order of "letters" in the DNA "recipe." The DNA sequence is the chemical structure that contains information.

Transformation – a procedure to transfer DNA into the cells of an organism. Can be done with Agrobacterium (most dicots), calcium chloride (bacteria), electroporation (any organism), or the particle gun (any organism).

Transgenic – an organism that has been modified by genetic engineering to contain DNA from an external source.

Vector - any DNA structure that is used to transfer DNA into an organism; most commonly used are plasmid DNA vectors or viruses.