The phrase "null mice" refers to lab mice that have been genetically modified so they lack a specific gene. These mice are used in scientific research to understand the function and importance of that gene. Full definition
«The J20 / caspase -2 null mice showed the same dendritic spine density and morphology as the normal mice — as opposed to the deficits in the J20 mice,» said co-lead author Julio Pozueta, PhD. (sciencedaily.com)
At 14 months, however, the J20 / caspase -2 null mice did significantly better in the water maze test than the J20 mice and similarly to the normal mice. (sciencedaily.com)
Irradiated Rassf1A null mice also showed increased tumor susceptibility, particularly to tumors associated with the gastrointestinal tract, compared with wild - type mice. (sanger.ac.uk)