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Transgenesis is the process of introducing an exogenous gene – called a transgene – into a living organism so that the organism will exhibit a new property and transmit that property to its offspring. Transgenesis can be facilitated by liposomes, plasmid vectors, viral vectors, pronuclear injection, protoplast fusion, and ballistic DNA injection.

Transgenic organisms are able to express foreign genes because the genetic code is similar for all organisms. This means that a specific DNA sequence will code for the same protein in all organisms. Due to this similarity in protein sequence, scientists can cut DNA at these common protein points and add other genes. An example of this is the "super mice" of the 1980s. These mice were able to produce the human protein tPA to treat blood clots.

Using plasmids from bacteria

The most common type of transgenesis research is done with bacteria and viruses which are able to replicate foreign DNA.^[1] The plasmid DNA is cut using restriction enzymes, while the DNA to be copied is also cut with the same restriction enzyme, producing sticky-ends. This allows the foreign DNA to hybridise with the plasmid DNA and be sealed by DNA ligase enzyme, creating a genetic code not normally found in nature. Altered DNA is inserted into Plasmid for replication.^[2]

Gene Transfer Technology

1. DNA Microinjection- 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. DNA microinjection does not have a high success rate (roughly 2% of all injected subjects), even if the new DNA is incorporated in the genome, if it is not accepted by the germ-line the new traits will not appear in their offspring. If DNA is injected in multiple sites the chances of over-expression increase.^[3]

2. Retrovirus-mediated gene Transfer- A retrovirus is a virus that carries its genetic material in the form of RNA rather than DNA. Retroviruses are used as vectors to transfer genetic material into the host cell. The result is a chimera, an organism consisting of tissues or parts of diverse genetic constitution. Chimeras are inbred for as many as 20 generations until homozygous genetic offspring are born.^[4]

3. Embryonic cell-mediated gene Transfer- The manipulated gene construct is inserted into totipotent stem cells, cells which can develop into any specialized cell. Cells containing the desired DNA are incorporated into the host’s embryo, resulting in a chimeric animal. Unlike the other two methods of injection which require live transgenic offspring for testing, embryonic cell transfer can be tested at the cell stage.

Pharming

Pharming is a portmanteau of "farming" and "pharmaceutical" and refers to the use of genetic engineering to insert genes that code for useful pharmaceuticals into host animals or plants that would otherwise not express those genes, thus creating a genetically modified organism (GMO).^[5] Pharming has gained application in biotechnology since the development of trangsgenic "super mice" in 1982. "Super mice" were genetically altered to produce the human drug, tPA (tissue plasminogen activator to treat blood clots), in 1987.^[6] Since the "super mice" pharming has come a long way. Using RNA interference scientists have produced a cow whose milk contains increased amounts of casein, a protein used to make cheese and other foods, and almost no beta-lactoglobulin, a component in milk whey protein that causes allergies.^[7]

"Pharming Examples:"^[8]

Haemoglobin as a blood substitute
human protein C anticoagulant
alpha-1 antitrypsin (AAT) for treatment of AAT deficiency
insulin for diabetes treatment
vaccines (antigens)
growth hormones for treatment of deficiencies
factor VIII blood clotting factor
factor IX blood clotting factor
fibrinogen blood clotting factor
lactoferrin as an infant formula additive

Diagram

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Note: New genotypes created with transgenic technologies also require multiple backcrossings. Furthermore, backcrossing does not account for the majority of time required to create, field test and release/commercialize a new variety.

References

[1] ttp://www.fas.org/biosecurity/education/dualuse/FAS_Jackson/1_A.html

[2] ttp://users.wmin.ac.uk/~redwayk/lectures/transgenic.htm

[3] ttp://www.actionbioscience.org/biotech/margawati.html

[4] ttp://www.actionbioscience.org/biotech/margawati.html

[5] ttp://en.wikipedia.org/wiki/Pharming_(genetics)

[6] ttp://users.wmin.ac.uk/~redwayk/lectures/transgenic.htm

[7] ttp://www.businessweek.com/news/2012-10-01/gene-modified-cow-makes-milk-rich-in-protein-study-finds

[8] ttp://people.ucalgary.ca/~browder/transgenic.html

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Revision as of 14:49, 19 February 2014 edit Melaen (talk \| contribs) Extended confirmed users 22,963 edits moved image (too large) - added secriond DIAGRAM like in the cisgenesis article ← Previous edit		Revision as of 08:29, 4 March 2014 edit undo Naapple (talk \| contribs) 690 edits link to genetically modified mouse Next edit →
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	'''Transgenesis''' is the process of introducing an [[Exogeny\|exogenous]] gene – called a [[transgene]] – into a [[living organism]] so that the organism will exhibit a new property and transmit that property to its [[offspring]]. Transgenesis can be facilitated by [[liposome]]s, [[plasmid vector]]s, [[viral vector]]s, [[Microinjection#Pronuclear Injection\|pronuclear injection]], [[protoplast fusion]], and [[gene gun\|ballistic DNA injection]].		'''Transgenesis''' is the process of introducing an [[Exogeny\|exogenous]] gene – called a [[transgene]] – into a [[living organism]] so that the organism will exhibit a new property and transmit that property to its [[offspring]]. Transgenesis can be facilitated by [[liposome]]s, [[plasmid vector]]s, [[viral vector]]s, [[Microinjection#Pronuclear Injection\|pronuclear injection]], [[protoplast fusion]], and [[gene gun\|ballistic DNA injection]].

	[[Transgenic organism]]s are able to express foreign genes because the [[genetic code]] is similar for all organisms. This means that a specific [[DNA sequence]] will code for the same [[protein]] in all organisms. Due to this similarity in protein sequence, scientists can cut DNA at these common protein points and add other genes. An example of this is the "super mice" of the 1980s. These mice were able to produce the human protein tPA to treat blood clots.		[[Transgenic organism]]s are able to express foreign genes because the [[genetic code]] is similar for all organisms. This means that a specific [[DNA sequence]] will code for the same [[protein]] in all organisms. Due to this similarity in protein sequence, scientists can cut DNA at these common protein points and add other genes. An example of this is the [[genetically modified mouse\|"super mice"]] of the 1980s. These mice were able to produce the human protein tPA to treat blood clots.