Genetic Modification (GM) is the process of changing or inserting genes. Genes carry the information about the different characteristics of an organism such as the colour of its leaves or how tall it can grow. These genes are made from a string of DNA, the material found in the cells of all living things which allows them to function, repair and reproduce themselves. Genetic Modification is done by altering DNA or by taking genes from one organism and putting them into another. Genes can be moved between organisms that are of the same or different species. For example, genes could be introduced from one plant to another plant, from a plant to an animal or from an animal to a plant. This altered genetic material is then called recombinant DNA
Why use genetic modification?
People have been breeding animals and plants for hundreds of years with the aim of developing or removing certain characteristics. Racehorses are bred to be faster and stronger and roses are bred to give a wider range of colours. The world’s main food crops have been chosen and bred to suit the countries and conditions they are grown in and make them more tasty.
Traditional breeding methods involving mixing thousands of genes, whereas genetic modification allows just one individual gene to be changed in a pre-determined way.
For example, herbicides are used to kill weeds in fields of crops but they can also affect the growth of the crops they are intended to protect. By using genetic modification, a gene with a particular characteristic, such as resistance to a specific herbicide, can be introduced into a crop plant. When that herbicide is sprayed on the field to kill the weeds, it will not hinder the growth of the crops.
Similarly, genetic modification can be used to reduce the amount of pesticide needed by altering a plant’s DNA so it can resist the particular insect pests that attack it. For example GM Maize and Cotton that resist their primary insect predator are widely used around the world . Laying hens have chicks that have been bred so that male and female chicks are born different colours. Only the females are required for egg production, so can be separated early.
How does it work?
Paste in pics from the GM crop display
To extract the gene from the original organisms enzymes called restriction endonucleases
are used. Restriction endonucleases are usually found in microorganisms. Specific restriction endonucleases cut DNA at a specific nucleotide sequences, these are called recognition sites. The enzymes cut in a staggered way so that a few base pairs are left exposed on each side of the double strand of DNA, these bases are complementary to each other and are referred to as sticky ends.
Once the gene is extracted it needs to be combined with a plasmid
which is also known as a vector
, since they add the new gene into a host cell transferring genes from one organism to another. Plasmids are found in bacteria and are double stranded circular bits of DNA, which are separate to the chromosomal DNA. They are used as vectors for the gene since they are small and replicate many times inside the bacteria and therefore produce many copies of the desirable gene. The gene is combined with the plasmid by using the same restriction endonuclease to cut open the plasmid that was used to extract the gene. Therefore both the plasmid and the gene have complementary sticky ends, and the bases join together with hydrogen bonds. The enzyme DNA ligase
will join the gene to the plasmid with phosphodiester bonds
The plasmid along with the inserted DNA is referred to as recombinant DNA
and it is then placed into bacterial cells. The bacterial cells are more permeable
to the plasmids if they are treated with calcium ions
. When the bacteria cells contain the recombinant DNA they are referred to as transformed cells
Not all of the bacteria cells will take up the recombinant DNA and these cells need to be separated from the transformed cells, which do. These can be separated by the use of a radioactive DNA probe
or genetic markers
such as a gene for antibiotic resistance. Once the transformed cells have been identified they need to be multiplied.
Introducing new genes into crop plants
The soil bacteria Agrobacterium tumefaciens
contains a plasmid called a Ti plasmid. This is used as the vector for the gene to be introduced into and returned into the Agrobacterium tumefaciens
. The transformed bacterium is introduced into leaf discs or isolated plant cells in a culture and the plasmid is transferred into the plant cells. These transformed plant cells are then grown into undifferentiated tissue and then in the right conditions are grown into plantlets, which are known as transgenic plants
GM foods used today
GM is increasingly recognised as being useful to us, but it needs safeguards.
All commercial tomatoes are genetically modified to avoid rotting after a few days in the shop.
The most widely used barley for beer making, Golden Promise was developed by bombardment with X-rays.
Some GM could be harmful to other plants or to us, so regulations are in place to keep GM development under close scrutiny.
Implications of gene technology
With the use of gene technology many questions are raised such as ‘Is this unnatural?’ and ‘Are we interfering with nature?’