TRANSGENICS

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Introduction to Genetically Modified Organisms (GMOS)

Introduction: A genetically modified organism (GMO) is an organism or microorganism whose

genetic material has been altered to contain a segment of DNA from another organism.

Modern recombinant DNA technology enables the “stitching together” of pieces of DNA, regardless of the source of the pieces. Since the 1980s, this technology has been used extensively in the lab by researchers for countless purposes: to make copies of genes or proteins, to determine gene function, to study gene expression patterns, and to create models for human disease.

One application has been to generate food crops that are modified in a way that is advantageous to either the producer or the consumer. Currently the GM crops on the market have bacterial genes introduced into their genomes that encode for pest or herbicide resistance.

In theory, this should cut down on the amount of chemicals a farmer needs to spray, but in practice that goal has not been realized as pests and weeds become resistant to the chemicals being used.

Transgenic Animals

A transgenic animal is one that carries a foreign gene that has been deliberately inserted into its genome. The foreign gene is constructed using recombinant DNA methodology

How are transgenic animals produced?

Since the discovery of the molecular structure of DNA by Watson and Crick in 1953, molecular biology research has gained momentum.

Scientists can now produce transgenic animals because, since Watson and Crick's discovery, there have been breakthroughs in:

    1. Recombinant DNA (artificially-produced DNA)     2. Genetic cloning     3. Analysis of gene expression (the process by which a gene

gives rise to a Protein)     4. Genomic mapping

Three basic methods of producing transgenic animals

1. DNA microinjection    2. Retrovirus-mediated gene transfer    3. Embryonic stem cell-mediated gene transfer

1(a). DNA Microinjection

1(a). Microinjection:Using fine tipped (0.5 - 1.0

micrometer diameter) glass needle or micropipette. 

This method of gene transfer is used to introduce DNA into large cells such as oocytes, eggs, and the cells of early embryo.

The mouse was the first animal to undergo successful gene transfer using DNA microinjection.6 This method involves:

transfer of a desired gene construct (of a single gene or a combination of genes that are recombined and then cloned) from another member of the same species or from a different species into the pronucleus of a reproductive cell .

The manipulated cell, which first must be cultured in vitro (in a lab, not in a live animal) to develop to a specific embryonic phase, is then transferred to the recipient female.

The Desired gene construct is injected in the pronucleus of a reproductive cell using a glass needle around 0.5 to 5 micrometers in diameter. The manipulated cell is cultured in vitro to develop to a specific embryonic phase, is then transferred to a recipient female.

1(b). Electroporation

1(b).Electroporation: The cells are placed in a

solution containing DNA and subjected to electrical shocks to cause holes in the membranes. The foreign DNA fragments enter through the holes into the cytoplasm and then to nucleus.

Electroporation is a physical transfection method that uses an electrical pulse to create temporary pores in cell membranes through which substances like nucleic acids can pass into cells.

It is a highly efficient strategy for the introduction of foreign nucleic acids into many cell types, including bacteria and mammalian cells.

2. Retrovirus-Mediated Gene Transfer 

A retrovirus is a virus that carries its genetic material in the form of RNA rather than DNA.

This method involves: Retroviruses used as vectors to transfer genetic material

into the host cell, resulting in a chimera, an organism consisting of tissues or parts of diverse genetic constitution

Chimeras are inbred for as many as 20 generations until homozygous (carrying the desired transgene in every cell) transgenic offspring are born

Life cycle of Retrovirus

Four classes of viral vector

Retrovirus- commonly used( Offspring’s derived from this

method are chimeric; not all cell carry the retrovirus i.e diverse genetic constitution)

Adenovirus Herpesvirus Adenoassociated Virus(AAV) Vectors

3. Embryonic Stem Cell-Mediated Gene Transfer 

Isolation of totipotent stem cells (stem cells that can develop into any type of specialized cell) from embryos.

The desired gene is inserted into these cells. Cells containing the desired DNA are incorporated

into the host’s embryo, resulting in a chimeric animal.

Unlike the other two methods, which require live transgenic offspring to test for the presence of the desired transgene, this method allows testing for transgenes at the cell stage.

Embryonic stem cellsFormation of gametocytesInjection into blastocystsInjection into foster mother

Formation of new individual

Applications

The benefits of these animals to human welfare can be grouped into areas:

Agriculture Medicine Industry

Medicine:- We can say that medicine is one field which has took benefit of transgenic animals most. Every year people die of kidney failure, heart failure and due to other organs failure. But now scientists have succeeded in producing transgenic animals like pigs which carry the organs needed for humans. Pig is responsible for providing the organs to the humans and these organs can be inserted into the human body through transplantation.

Transgenic animals have already helped in developing certain growth hormones. For this purpose, special genes are inserted in the milk of the cow, which increase the production of the milk. Similarly various genetic and hereditary diseases like cystic fibrosis and phenylketonuria can be treated by manufacturing milk which is developed with trans genesis. 

Human gene therapy has provided opportunities for medicine that in a certain genetic or acquired disease, damaged genes can be replaced with the healthy genes and their function is secured. 

Agriculture:- Agriculture is another field which has taken advantage of transgenic animals. In livestock, when transgenic animals are bred with the normal animals, the generation produced contains healthy organs, meat and milk. Transgenic techniques have made quick production of animals while traditional methods of animals breeding are time taking. Quality of the animals also increases and they are the source of providing good quality food to humans in the form of milk and meat. 

Industry:- Two scientists of Canada succeeded in inserting spider genes in the goats who gave milk. The goats produced silk with the milk in large amounts. It was a good source of economy for the industrialists. Polymer strands of the silk were extracted from the milk and light threads were made. This thread could be used in the making uniforms of soldiers and also the tennis rockets. 

Conclusion:-

Transgenic animal techniques have developed rapidly and provided more and improved platforms for the preparation of transgenic animals since their emergence.

All of these developments will provide new ideas and bring forth important changes in fields like medicine, health and livestock improvement.

In particular, the economic and social benefits from the production of bioreactors, drug production, and organ culture for human transplantation will be great.