Mammals that glow fluorescent colors. A fearless mouse. A goat that spins spider silk. These animals do not exist naturally, but thanks to transgenesis, a process in which foreign genes are inserted into an animal's DNA, they are around today. Scientists create so-called transgenic animals to investigate disease treatments, produce natural material and expand scientific knowledge. The general principle of producing a GMO(genetically modified organism)is to add new genetic material into an organism's Genome. This is called genetic engineering and was made possible through the discovery of DNA and the creation of the first recombiant DNA molecules by Paul Berg in 1972. To date, there are three basic methods of producing transgenic animals DNA microinjection, Retrovirus-mediated gene transfer, embryonic stem cell-mediated gene transfer. DNA Microinjection. The mouse was the first animal to undergo successful gene transfer using DNA microinjection 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. Retrovirus-Mediated Gene Transfer The second method produces chimeras, altered animals with mixed DNA.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. The method was successfully used in 1974 when...
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