The ability to generate a mouse with a targeted mutation in a desired gene
has been one of the most important advances in understanding the function of
gene products. Not only can gene disruption demonstrate the function of genes,
but by disrupting cell development or survival it can also demonstrate the function
of specific cell types. Some knockout mice are murine models of human
genetic diseases and have proven that a single gene defect is capable of causing
disease. In addition, the crossing of mice that are heterozygous or homozygous
for specific gene mutations provides important information on human diseases
that are caused by multiple genetic defects. In genetic terms, targeted gene
disruption is directly complementary to (and arguably more direct than) using
mutant strains of mice with a known phenotype to map and identify the diseasecausing
genes