Floxed

Floxed is a term used in genetics to describe a DNA sequence that is flanked by loxP sites, a configuration created to enable controlled genetic modification. The sequence between the loxP sites can be manipulated by the Cre recombinase enzyme, allowing researchers to delete, invert, or sometimes transpose the intervening segment under specific conditions. When the two loxP sites are in the same orientation, Cre recombinase excises the intervening DNA, leaving a single loxP site behind.

The term arises from the combination of “loxP” and the common suffix used for genetic modifications. A gene or exon that is surrounded by loxP sites is referred to as a floxed allele. This setup is central to Cre-loxP systems, which are widely used to generate conditional mutations in model organisms, particularly mice. By coupling Cre expression to tissue-specific promoters or to inducible systems, researchers can achieve spatial or temporal control over gene inactivation or modification.

Common applications include conditional knockouts, where a gene is inactivated only in certain tissues or at particular developmental stages, and reporter alleles, where a floxed stop cassette controls the expression of a reporter gene such as GFP. Inducible Cre variants, such as Cre-ERT2 that responds to tamoxifen, add temporal control to the system. While floxed alleles are powerful tools, researchers must consider recombination efficiency, potential mosaicism, and the possibility of unintended effects if loxP sites lie near regulatory elements.

In summary, floxed describes a DNA segment flanked by loxP sites enabling Cre-mediated, conditionally controlled genetic modification.