gene knockout

A gene knockout is what happens when scientists switch a gene off to see what it was doing. The logic is like removing one part from a machine and watching what breaks: if turning off a gene makes an organism lose its sense of smell, that gene probably helps build the smell system.

In practice, a knockout disrupts a gene so it can no longer make a working product. A common modern route is to cut the gene with a tool like CRISPR-Cas9, then let the cell's error-prone non-homologous end joining repair the break — the small insertions or deletions it leaves often shift the reading frame and destroy the protein. Older methods used homologous recombination to replace the gene with an inactive cassette.

Knockouts are a cornerstone of reverse genetics: start from a gene, remove it, and read off its function from the resulting phenotype. Caveats matter, though — some genes have backups that mask the effect, knocking out an essential gene can be lethal, and the change may differ between cells, tissues, or whole-organism knockouts.