A behaviour mutation is a genetic mutation that alters genes that control the way in which an organism behaves, causing their behavioural patterns to change. A mutation is a change or error in the genomic sequence of a cell. It can occur during meiosis or replication of DNA, as well as due to ionizing or UV radiation, transposons, mutagenic chemicals, viruses and a number of other factors. Mutations usually (but not always) result in a change in an organisms fitness. These changes are largely deleterious, having a negative effect on fitness; however, they can also be neutral and even advantageous.