text: A knockout moss is a kind of genetically modified moss. One or more of the moss's specific genes are deleted or inactivated ("knocked out"), for example by gene targeting or other methods. After the deletion of a gene, the knockout moss has lost the trait encoded by this gene. Thus, the function of this gene can be inferred. This scientific approach is called reverse genetics because the scientist wants to understand the function of a specific gene. In classical genetics, the scientist starts with a phenotype of interest and searches for the gene that causes this phenotype. Knockout mosses are relevant for basic research in biology as well as in biotechnology.