ABSTRACT
The characterization of a gene by cloning and sequencing leads to comparison of its sequence with those deposited in international data banks. In some cases, the gene identified presents similarities with a gene of another organism coding for a protein of known function. In other cases, the sequence studied has no similarity with any known sequence and the function of the protein coded by that gene remains unknown. In these two types of situations, it remains necessary either to demonstrate the biological function identified by similarity experimentally or to create an individual deficient in the function of the unidentified gene. In other words, the role of the gene must be confirmed or determined. The gene knock-out technique makes it possible to obtain a transgenic organism that no longer expresses the target gene. The phenotype of this mutant, which lacks a function, will thus indicate the role of the protein coded by the gene that is being studied.
