In biotechnology a knockout refers to an organism which has been genetically altered in such a way that one of its genes is missing or inactive due to a mutation, or its complete deletion. Since the discovery of genes, scientists have been determined to learn the structure and function of all their protein products. The construction of knockouts is one technique for doing this. Knockouts can be deliberately made using molecular techniques such as site-directed mutagenesis, or they can be acquired by the selection of natural mutants. Knockouts are used to study the function of specific genes, detect their protein products, and link them to diseases that arise when their function is inadequate.
Knockout mice are a common tool for studying genes in the laboratory. Microorganisms are also frequently used for studying gene function, because knockouts are easy to make using plasmid transformation and phage transduction methods. While knockouts are often useful tools for studying gene products and their function, in some cases the knockout can be lethal and the organism does not live long enough for further investigation to take place.