A
knock-out mouse (or
knockout mouse) is a
mouse with a
gene knockout, a
gene that was deactivated, either on purpose using
genetics methods, or by chance mutation (rarely used). Usually, the purpose of creating such mice is to see what effect the missing gene function has on the
phenotype. As mice and humans share many genes, studying of knock-out mice can improve knowledge of the workings of a similar gene in humans. Also, (human) diseases (for example,
cancer or
Alzheimer's disease) can be simulated by gene knock-outs in mice, allowing for mass testing of possible treatments.