Taking genes from one organism and
putting them in another where they work as normal still sounds like
something from a science fiction story. But far from being the product
of a writer's imagination, genetic modification is well and truly
science fact!
The first way developed of transferring genes from one organism
to another is the method described on the poster,
in "How does genetic engineering work?"
and in the genetic engineering animation.
But a number of other ways have been developed, and these are all
used in different situations to transfer genes from one organism
to another for a variety of different reasons.
| Using viruses |
| In this method, the desired gene is inserted into the
genetic material of a virus. The virus is then allowed
to infect the cells where the gene is needed. When the
viral DNA infects the host cell, the desired gene goes
with it and is incorporated into the host DNA. The virus
itself is modified so that although it can carry the new
gene into the cell, it cannot take over the cells metabolism
to make thousands of copies of itself. As the cells then
replicate normally, the new gene replicates as well and
begins to produce proteins. |
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| Microinjection |
| This is one of the simplest ways of manipulating the
genes. The desired gene is removed from the original cell
using a microscopically fine glass micropipette. It is
then injected directly into the nucleus of the recipient
cell. The injected gene incorporates itself into the host
genetic material and begins to code for proteins. The
main limitation to this technique is that not all cells
are big enough to allow the micropipettes to penetrate
without damaging the cell. |
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| Electroporation |
| This technique involves making pores appear artificially
in the membranes of the host cell so that the new DNA
can enter the cell. The pores are created by exposing
the cells to a weak electrical current. Amazingly, once
a gene is inside a cell it will often find its way into
the nucleus, because although a whole chromosome cannot
escape through the nuclear pores, single genes can fit
through. |
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| Chemical poration |
| This is another technique which relies on making artificial
pores in the cell membrane to allow the new genes to go
in. This method involves bathing the cells in a chemical
solution which causes pores to appear in the cell membrane. |
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| Laser poration |
| Here, pores are created artificially using tiny laser
beams to create holes in the membrane of the host cell
before the new genes are introduced. |
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| Gene scissors |
| In this technique lasers are used to cut genes or larger
chunks of chromosomes out of the DNA of one organism.
They can also cut open the DNA of the recipient organism
to make it easier for the new genes to be incorporated. |
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| Bioballistics |
| Yet another technique that sounds pure science fiction,
scientists have found a way of firing new genes directly
into the host cell. For example, in one method tiny metal
slivers, much smaller than a cell in size, are coated
with the gene which is to be engineered into another organism.
The gene-coated metal slivers are then added to a cartridge
which is loaded into a shotgun and fired!! A metal plate
with minute holes in it acts like a ballistic sieve, stopping
the cartridge but allowing the slivers to pass through
and into a solution of cells on the other side. Once in
the cells, the genetic material is carried into the nucleus
and is incorporated into the host genes, where as usual
it directs protein synthesis. |
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