Gene technology

How gene technology developed

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Why we can modify genes

Genes have three basic parts – an 'on' switch, an 'off' switch and the region that codes for a protein.

For a gene to work, it must have all three basic parts, but they do not have to be from the same organism. This is because the DNA of all living things is made up of the same four molecular components called nucleotides.

Each of the four nucleotides has a different base, called adenine, guanine, thymine and cytosine.

This means the gene for a particular characteristic that has been identified in one organism can be permanently introduced into another organism after being modified so it will be recognised by the new organism, which then adopts this new characteristic.

For example, you could take the protein-producing part of a gene in corn that produces vitamin A and combine this with the on and off gene switches from a seed gene from rice. The result would be a gene that produces more vitamin A in rice seed.

DNA strand

Inserting the gene

When a gene has been modified it is inserted into the DNA of the new organism, so it becomes a permanent part of the organism's genetic makeup.

Scientists do this by inserting the gene into individual cells from the new organism. How scientists do this depends on the type of organism. They may use:

  • a fine tube to microinject the gene into an animal egg
  • a miniature gun that shoots the gene, attached to tiny gold or tungsten particles, into the cell (this technique is referred to as biolistics)
  • a bacterium (Agrobacterium) that transfers DNA to plant cells
  • calcium silicate crystals to puncture holes in the cells to allow DNA to enter
  • a virus to carry the genes into the cells of the organism 
  • an electric shock to encourage cells to take up DNA.  

The most commonly used techniques in plants are biolistics and Agrobacterium.

A mark of success

Not all cells will take up a modified gene, so scientists need to be able to select those cells that have the new gene from those that don’t. To do this, scientists use selectable marker genes, which are like flags that signal whether a cell has taken up the modified gene.

The marker gene and the gene scientists are interested in are transferred together into the new organism.

When a gene has been modified it is inserted into the DNA of the new organism, so it becomes a permanent part of the organism's genetic makeup.

Marker genes code for characteristics that can be easily identified, such as the ability to survive in the presence of an antibiotic that has been added to the medium surrounding the cells.

In this case, any cells that have not taken up the modified gene and its associated marker gene will die, leaving only those cells that have been genetically modified.

Growing organisms from cells

Cells that have successfully taken up the new gene are grown into organisms. For example, if the new gene has been put into a plant cell, cells are grown in a 'tissue culture'.

In the laboratory the plant cells are made to divide, grow and develop shoots and roots to form a whole plant. Regenerating plants from individual cells is a slow process, but once the plants are big enough they can be put into pots and grown in glasshouses.

If the new gene has been inserted into an animal egg, the egg is implanted into a female animal. Because the gene was inserted into the DNA at the egg stage, when the cell divides, every cell in the growing embryo will contain the new DNA.

Silencing genes

Gene technology can introduce new genes into an organism and also silence or turn off an existing gene in an organism. 

The silencing of specific genes can be used to make plant food products with different compositions that are beneficial to humans.

This technology can also be used to silence viral genes thereby preventing infections in animals and plants.

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