Cloning of a Gene

Cloning of a Gene

To clone a gene (assuming that a plasmid is to be the vector), a restriction enzyme is used to cleave plasmid DNA and to cleave
foreign DNA. The "sticky ends" produced facilitate the insertion of foreign DNA into vector DNA. The foreign gene is sealed into the vector DNA by DNA ligase.

A genomic library can be used as a source of genes to be cloned. A radioactive or fluorescent probe is used to identify the
location of a single gene among the cloned fragments of an organism's DNA. The polymerase chain reaction (PCR) uses the
enzyme DNA polymerase to carry out multiple replications of tar- get DNA.

DNA can be subjected to DNA fingerprinting. After the DNA of an organism is treated with restriction enzymes, the fragments are subjected to gel electrophoresis. If the entire genome is used for fingerprinting, the use of probes results in a distinctive pattern that can be recorded on X-ray film. If DNA fingerprinting follows PCR, no probes are needed because of the limited amount of DNA involved. PCR plus analysis, which may even involve sequencing the bases of a DNA segment, has proved to be invaluable.