Gene knockout

Knockout genes are produced as follows:

The nucleotide base sequence of a specific gene is altered, often by inserting a specially designed DNA chain into the gene. The altered gene will now no more be able to perform its original function, which is often to code for one or more proteins through RNA transcription and translation.

To this end an artificial DNA probe[?] (small base sequence) is inserted into the cell. This probe is designed such that it will bind only to parts of the targeted gene. Through recombination parts of the probe will become part of the original gene, thus rendering it ineffective.

Moreover the inserted sequence, called a 'cassette', may contain a new functional gene itself which introduces an new trait that allows easy selection of individuals where the knockout was performed successfully. For instance, in bacteria a new gene might be introduced that introduces resistance to some antibiotic. All bacteria without the new insert are then easily removed by adding that antibiotic.

In plants and animals, which have chromosomes that contain two or more similar DNA sequences, further selective breeding is used to make the alteration replace all copies of the targeted gene. Only then will all gene activity stop, and can all resulting changes be studied.