Delaying the knockout punch

The drawback of most techniques used to create knockout mice is that the gene is removed before conception. As a result, many animals die before birth and can't be studied. In addition, some that survive have compensated for the missing gene, confounding the purpose of the knockout experiment. But a "conditional" method of knocking out genes, discovered in 1985 by a DuPont scientist, has offered researchers a solution.

The method, dubbed Cre-lox, uses Cre recombinase enzyme to excise part of a gene. Using transgenic techniques, two Cre recognition sites, also called loxP sites, are inserted in the target gene. Then, after the mouse is grown, the researcher turns on Cre. Cre removes the portion of the gene between the two loxP sites, effectively knocking out the gene...