A strain of mice widely studied as a model for cystic fibrosis. These mice are generated from embryonic stem cells in which the CFTR (cystic fibrosis transmembrane conductance regulator) gene is inactivated by gene targeting. As a result, all mice have one copy of this altered gene in all their tissues. Mice homozygous for the disrupted gene exhibit many features common to young cystic fibrosis patients, including failure to thrive, meconium ileus, and alteration of mucous and serous glands.