First step to cloning a gene is making a library of genetic material of chosen organism, that will represent it’s whole genome. Then desired gene must be identified. Characteristic features that enables finding the gene are it’s DNA sequence and protein the gene encodes for. When the DNA sequence is known suitable probes can be used. Sometimes protein provides the cell with a feature that enables easy identification. Antibodies are often used when searching for a certain protein.

Probes enable detecting certain DNA sequences. Probe is nucleic acid (cDNA or RNA) complementary to the searched one. Usually it is labeled by radioactive isotope that makes finding the fragment that combined with the probe possible. DNA chains in the cell are first unwound. Then the probe is added so that it can join the complementary sequence. Exposure to photographic film enables localization of the probe and searched fragment of DNA.

After identifying the cell that contains desired gene it is multiplied in laboratory. It leads to origination of clones – genetically identical cells. At last preparation is purified and nucleic acids for further inquiring are obtain.