Transgenic Animals
Transgenic Animals are those genetically modified animals in which foreign genes have been inserted, the gene which is inserted is known as a transgene and the process is known as transgenesis. This is the technique in which desired gene of interest is inserted in the target animal’s genome which alters the genetic makeup of that genome. Previously selective breeding techniques were used to improve genetic traits but now transgenesis is used to enhance the genetic characteristics of the genome of the target animals.
Methods of Gene Transfer
The common techniques of gene transfer to produce
transgenic animals are:
Physical method of gene transfer
Physical methods can be performed by particle
bombardment, electroporation, Ultrasonic waves, and DNA microinjection. It is
a direct method of gene transfer and is applied to a variety of animal species.
DNA microinjection involves a single gene or selected gene construct from
another specie or the same specie with a different member that is directly injected into the
pronucleus of the fertilized ovule.
The expression of the gene in another organism would be
unknown for example the inserted gene would be over-expressed, under-expressed, or would
be unique to the animal species showing similar characteristics as the host specie. The fertilized ovule is afterward placed in the host female animal.
This was the first technique performed which get successful on animals.
The first transgenic animal cloned was Dolly sheep. Dolly
sheep were produced through the electroporation method. An unfertilized egg was taken
and the nucleus was removed and injected into the udder cells of white sheep. Electric
pulses were given to fuse the cells of white sheep with the enucleated eggs of black
sheep. The embryo was produced which was cultivated for one week. Then embryo
was inserted into different black sheep which gave birth to dolly sheep.
Chemical Method of gene transfer
Chemical transfection is one of the methods of gene
transfer. The target DNA is introduced in the presence of calcium phosphate. DNA
is absorbed and precipitated by the use of calcium phosphate. DNA is catalyzed
through the cross-membrane which facilitates DNA uptake. Mammalian cells
present in culture media take the foreign DNA.
Vector-based Gene transfer
Different vectors are used to transfer genes such as
viral vectors, and bacterial vectors. Foreign DNA can be introduced to animal
cells through viruses. The viruses have the capacity to transfect the host cell,
express themselves, and multiply within the host cell. Bacterial vectors can
also be used to infect target DNA into the host cell.
Retroviral-based Gene transfer
The most common method of gene transfer is Retrovirus gene transfer. Retroviruses are RNA-based vectors that are used to transfer genes of interest into host organisms because of their ability to transfect host cells. This technique uses retrovirus to infect the host cell. During transfection, retroviral RNA is converted to DNA which is then introduced into the foreign DNA of the host organism.
The
offspring produced in this technique would be in a chimeric condition which
indicates that not all cells contain retrovirus because retrovirus incorporates
transgene into a few of the germ cells. These chimeras specie produce are cross-bred for several generations and if the transgene gets incorporated in every
cell, it will express in every cell resulting in homozygous transgenic animals.
Embryonic Stem cell gene transfer
This technique inserts the target DNA sequence (transgene) through in vitro embryonic stem cells. Stem cells are an undifferentiated
mass of cells that can develop into any cell, resulting in the development of a whole
organism. At the embryonic stage of development, the tissue of the desired organism
is integrated into an embryo. This technique is effective on mice. This method is
helpful in targeting specific gene mutations.
Genetically modified animals |
Applications of Transgenic Animals
The vast applications of transgenic animals for the
benefit of human welfare have been classified into three groups:
Agriculture
Medical
Industrial
Agricultural Applications
Selective breeding allows producing animals with desired features such as increased milk and meat production, better nutritional food, and a high growth rate. Previously conventional breeding was labor-intensive, time-consuming, and require more force to be performed. But nowadays, due to the advancement in technology, farming techniques have become precise and quicker.
Genetic engineering has
enabled farmers to boost production and increase livestock growth. For Example, transgenic
cows produce more milk with less lactose. Cattle with goats and sheep produce
more meat and sheep produce more wool.
Some of the animals have developed in such a way
that they are immune to diseases while in past this was impossible such as pigs
that are resistant to flu. Scientists are still striving to breed
disease-resistant organisms.
Medical Applications
The milk-producing transgenic
cows have benefited in many ways such as by producing products like insulin,
growth hormone, and blood anti-clotting agents. The chemical which promotes the
growth of red blood cells is produced by transgenic cows. Studies are being
conducted to produce milk by transgenesis for the treatment of genetic
disorders like phenylketonuria, and cystic fibrosis. These transgenic animals are
used as models for the treatment of disorders, and for the creation of
pharmaceutical products.
One of the medical
applications is gene therapy a person who has a defective gene can be
placed with a normal copy of the gene. Therefore, these animals examine how genes
are regulated and how they affect the body.
Transgenic mice have been useful in developing cures for many genetic
disorders. A calf with a transgene has been created that helps in the formation of human
red blood cells.
Transgenic animals are used
as research models for studying drugs and their effects. Before a particular
drug or vaccination is given to humans, it is first tested for safety on
transgenic animals as model organisms. By
inserting the genes in transgenic
animals, scientists can find the gene expression of a particular gene.
Industrial Applications
In Canada, they perform an
experiment in which spider silk genes were taken from spiders and inserted in goats to produce transgenic goats. This goat produces silk along with milk. Scientists can
secrete silk strands from the body of a goat. These silk strands from milk have been
extracted and weaved into a thread to produce materials that would be used in
making things like military uniforms, tennis rackets, and medical microsurgical
products.
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