APPLICATIONS RECOMBINANT DNA TECHNOLOGY (rDNA):
Recombinant DNA technology-refers to the creation of new combinations of DNA
segments that are not found together in nature. The isolation and manipulation of genes
allows for more precise genetic analysis as well as practical applications in medicine,
agriculture, and industry.
Recombinant DNA molecules- which sometimes called chimeric DNA are DNA
molecules formed by laboratory methods of genetic recombination (such as molecular
cloning) to bring together genetic material from multiple sources, creating sequences
that would not otherwise be found in biological organisms. Recombinant DNA is
possible because DNA molecules from all organisms share the same chemical
structure. They differ only in the nucleotide sequence within that identical overall
Photograph above is of GloFish, the first genetically modified animal to be sold as a
pet. The GloFish is a patented and trademarked brand of genetically modified (GM)
fluorescent fish. GloFish are a type of transgenic zebrafish (Danio rerio) that have been
modified through the insertion of a green fluorescent protein (gfp) gene. Not all GloFish
are green, however. Rather, there are several gfp gene constructs, each encoding a
different colored phenotype, from fluorescent yellow to fluorescent red
APPLICATIONS OF RECOMBINANT DNA TECHNOLOGY:
The most common application of recombinant DNA is in basic research, in which
the technology is important to most current work in the biological and biomedical
sciences. Recombinant DNA is used to identify, map and sequence genes, and to
determine their function. rDNA probes are employed in analyzing gene expression
within individual cells, and throughout the tissues of whole organisms.
Recombinant proteins are widely used as reagents in laboratory experiments and to
generate antibody probes for examining protein synthesis within cells and
organisms. Many additional practical applications of recombinant DNA are found
in industry, food production, human and veterinary medicine, agriculture, and
bioengineering. Some specific examples are identified below;
A) IN MEDICINE
Recombinants DNA technology or Genetic engineering has resulted in a series of
medical products. Multiple varieties of proteins are created from recombinant
DNA technology and it is used for medications. Some can be extracts from
humans, such as human growth hormone (rHGH), human insulin, folliclestimulating hormone (FSH) and factor VIII. Other proteins, when used as
medication, only have recombinant DNA as a source, such as with erythropoietin.
It has brought many revolutionary changes in the field of medicine and introduced
such methods of treating diseases and delivering the drug.
I) Recombinant human growth hormone (HGH, somatotropin)
Administered to patients whose pituitary glands generate insufficient quantities to
support normal growth and development. Before recombinant HGH became
available, HGH for therapeutic use was obtained from pituitary glands of cadavers.
This unsafe practice led to some patients developing Creutzfeldt-Jacob disease.
Recombinant HGH eliminated this problem, and is now used therapeutically. It has
also been misused as a performance enhancing drug by athletes and others.
II) Recombinant human insulin
Almost completely replaced insulin obtained from animal sources (e.g. pigs and
cattle) for the treatment of insulin-dependent diabetes. A variety of different
recombinant insulin preparations are in widespread use. Recombinant insulin is
synthesized by inserting the human insulin gene into E. coli, which then produces
insulin for human use.
III) Recombinant blood clotting factor VIII
A blood-clotting protein that is administered to patients with forms of the bleeding
disorder hemophilia, who are unable to produce factor VIII in quantities sufficient
to support normal blood coagulation. Before the development of recombinant
factor VIII, the protein was obtained by processing large quantities of human blood
from multiple donors, which carried a very high risk of transmission of blood
borne infectious diseases, for example HIV and hepatitis B.
IV) Recombinant hepatitis B vaccine
Hepatitis B infection is controlled through the use of a recombinant hepatitis B
vaccine, which contains a form of the hepatitis B virus surface antigen that is
produced in yeast cells. The development of the recombinant subunit vaccine was
an important and necessary development because hepatitis B virus, unlike other
common viruses such as polio virus, cannot be grown in vitro.
V) Diagnosis of infection with HIV
Each of the three widely used methods for diagnosing HIV infection has been
developed using recombinant DNA. The antibody test (ELISA or western blot)
uses a recombinant HIV protein to test for the presence of antibodies that the body
has produced in response to an HIV infection. The DNA test looks for the presence
of HIV genetic material using reverse transcriptase polymerase chain reaction (RTPCR). Development of the RT-PCR test was made possible by the molecular
cloning and sequence analysis of HIV genomes.
Accordingly, the development of genetically engineered animals has overcome the
hyper acute rejection barrier, with acute humoral xenograft rejection (AHXR)
currently remaining the most important immunological obstacle. At this stage, a
better control of the elicited anti-pig humoral immune response and avoidance of
coagulation disorders are the two primary research fronts being pursued in order to
overcome AHXR. Nonetheless, it is encouraging that porcine xenografts can
sustain the life of non-human primates for several months.
VII) Human gene therapy
Human gene therapy involves adding a normal copy of a gene (transgene) to the
genome of a person carrying defective copies of the gene. The potential for
treatments for the 5,000 named genetic diseases is huge and transgenic animals
could play a role. For example, the A. I. Virtanen Institute in Finland produced a
calf with a gene that makes the substance that promotes the growth of red cells in
humans. Hence a transgenic cow exists that produces a substance to help human
red cells grow.
VIII) Control of Mosquito transmitted infections
In 2010, scientists created "malaria-resistant mosquitoes" in the laboratory. The
World Health Organization estimated that Malaria killed almost one million people
in 2008.Genetically modified male mosquitoes containing a lethal gene have been
developed in order to combat the spread of Dengue fever. Aedes aegypti
mosquitoes, the single most important carrier of dengue fever, were reduced by
80% in a 2010 trial of these genetic modified (GM) mosquitoes in the Cayman
Islands. Between 50 and 100 million people are affected by Dengue fever every
year and 40,000 people die from it.
Other applications of recombinant DNA technology in medicine are productions of
following useful products;
Tumor necrosis factor. Treatment for certain tumor cells
Interleukin-2 (IL-2). Cancer treatment, immune deficiency, and HIV
Prourokinase. Treatment for heart attacks
Taxol. Treatment for ovarian cancer
Interferon. Treatment for cancer and viral infections.
B) IN AGRICULTURE
Crop plants have been and continue to be the focus of biotechnology as efforts are
made to improve yield and profitability by improving crop resistance to insects and
certain herbicides and delaying ripening (for better transport and spoilage
resistance). The creation of a transgenic plant, one that has received genes from
another organism, proved more difficult than animals. Unlike animals, finding a
vector for plants proved to be difficult until the isolation of the Ti plasmid,
harvested from a tumor-inducing (Ti) bacteria found in the soil. The plasmid is
“shot” into a cell, where the plasmid readily attaches to the plant's DNA. Although
successful in fruits and vegetables, the Ti plasmid has generated limited success in
I) Golden rice
A recombinant variety of rice that has been engineered to express the enzymes
responsible for β-carotene biosynthesis. This variety of rice holds substantial
promise for reducing the incidence of vitamin A deficiency in the world's
population. Golden rice is not currently in use, pending the resolution of regulatory
Photograph above show Golden rice (right) compared to white rice (left)
II) Herbicide-resistant crops
Commercial varieties of important agricultural crops (including soy, maize/corn,
sorghum, canola, alfalfa and cotton) have been developed that incorporate a
recombinant gene that results in resistance to the herbicide glyphosate, and
simplifies weed control by glyphosate application. These crops are in common
commercial use in several countries.
III) Insect-resistant crops
Bacillus thuringeiensis is a bacterium that naturally produces a protein (Bt toxin)
with insecticidal properties. The bacterium has been applied to crops as an insectcontrol strategy for many years, and this practice has been widely adopted in
agriculture and gardening. Recently, plants have been developed that express a
recombinant form of the bacterial protein, which may effectively control some
insect predators. Environmental issues associated with the use of these transgenic
crops have not been fully resolved.
Photograph above show Kenyans examining insect-resistant transgenic Bt corn
C) IN ANIMAL HUSBANDRY
Neither the use of animal vaccines nor adding bovine growth hormones to cows to
dramatically increase milk production can match the real excitement in animal
husbandry: transgenic animals and clones.
I) Transgenesis will allow larger herds with specific traits
Farmers have always used selective breeding to produce animals that exhibit
desired traits (e.g., increased milk production, high growth rate). Traditional
breeding is a time-consuming, difficult task. When technology using molecular
biology was developed, it became possible to develop traits in animals in a shorter
time and with more precision. In addition, it offers the farmer an easy way to
II) Improve the size and quality of livestock genetically.
Transgenic cows exist that produce more milk or milk with less lactose or
cholesterol, pigs and cattle that have more meat on them, and sheep that grow more
wool. In the past, farmers used growth hormones to spur the development of
animals but this technique was problematic, especially since residue of the
hormones remained in the animal product.
III) Disease-resistant livestock
Scientists are attempting to produce disease-resistant animals, such as influenzaresistant pigs, but a very limited number of genes are currently known to be
responsible for resistance to diseases in farm animals.
Photograph above show transgenic casein cows
D) IN FOOD INDUSTRY
Found in rennet, is an enzyme required to manufacture cheese. It was the first
genetically engineered food additive used commercially. Traditionally, processors
obtained chymosin from rennet, a preparation derived from the fourth stomach of
milk-fed calves. Scientists engineered a non-pathogenic strain (K-12) of E. coli
bacteria for large-scale laboratory production of the enzyme. This
microbiologically produced recombinant enzyme, identical structurally to the calf
derived enzyme, costs less and is produced in abundant quantities. Today about
60% of U.S. hard cheese is made with genetically engineered chymosin. In 1990,
FDA granted chymosin "generally-recognized-as-safe" (GRAS) status based on
data showing that the enzyme was safe.
E) INDUSTRY APPLICATION
I) Uses in industry include material fabrication
In 2001, two scientists at Nexia Biotechnologies in Canada spliced spider genes
into the cells of lactating goats. The goats began to manufacture silk along with
their milk and secrete tiny silk strands from their body by the bucketful. By
extracting polymer strands from the milk and weaving them into thread, the
scientists can create a light, tough, flexible material that could be used in such
applications as military uniforms, medical microsutures, and tennis racket strings.
II) Uses in determining safety tests of chemicals
Toxicity-sensitive transgenic animals have been produced for chemical safety
testing. Microorganisms have been engineered to produce a wide variety of
proteins, which in turn can produce enzymes that can speed up industrial chemical