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Humans can use advances in DNA technology to manipulate DNA within the laboratory and improve micro-organisms.

During recombinant DNA technology a fragment of DNA can be cut out and inserted into a vector. The vector is then used to carry this foreign genetic information into another cell. Examples of vectors include both plasmids and artificial chromosomes.

Restriction endonucleases are a group of enzymes that can recognise and cut specific sequences of DNA into fragments with sticky ends. These are pieces of DNA that have unpaired nucleotides at the end of them.

These enzymes are important as they allow for specific genes to be cut out of a source chromosome. They also cut bacterial plasmids.

Using the same restriction endonuclease enzyme to cut open the plasmid as is used to cut the gene from the chromosome results in complementary sticky ends being produced.

Ligase is an enzyme that is able to join two different fragments of DNA together. The sticky ends of the DNA fragments are complementary to each other, allowing ligase to bind them together, sealing the gene into the plasmid.

When larger fragments of DNA are required to be inserted into another cell an artificial chromosome will be used as a vector instead of a plasmid. A marker gene can be used to ensure that the fragment has been inserted into the vector successfully.

Recombinant plasmids and artificial chromosomes contain restriction sites, these contain target sequences of DNA where a specific restriction endonuclease will cut. Regulatory sequences can also be found on plasmids and artificial chromosomes which control gene expression.

The origin of replication allows the plasmid or artificial chromosome to self-replicate. Selectable markers are genes that give resistance to selective agents e.g. antibiotics that would normally kill the micro-organism or prevent it from growing.

Selectable marker genes can also be used to ensure that only the micro-organisms that have taken up the vector will grow when the selective agent is present. For example antibiotic resistance genes can be used to protect the recombinant cells from an antibiotic that is used as a selective agent. The untreated cells will be killed off or prevented from growing.

Some genes are inserted to stop the micro-organism from spreading into an external environment. This acts as a safety measure that decreases the chances of an uncontrollable outbreak of a micro-organism.