Infographic: The Cre-lox System Explained

Cre-loxP recombination allows scientists to excise, insert, or invert specific DNA segments with unprecedented accuracy.1,2  This works through two key components: a Cre recombinase and loxP sequence recognition sites. The Cre enzyme identifies pairs of loxP sites (arrowheads), which flank (flox) the DNA, and catalyzes reciprocal DNA recombination between the two sites to excise a small piece of DNA.

     Infographic showing the breeding schematic to generate Cre-loxP tissue-specific knockout mice.

To generate a tissue specific knockout mouse, researchers breed a mouse bearing a Cre transgene under a tissue- or cell-type specific or inducible promoter (A) with a homozygous floxed mouse (B).

The offspring are heterozygous for the floxed target gene (C) and breed with the homozygous floxed mouse (B).

The resulting experimental mouse is hemizygous for Cre and homozygous for loxP (D). This is the necessary genotype required to conditionally knock out the target gene in the specific tissue.


  1. Saur B. Functional expression of the cre-lox site-specific recombination system in the yeast Saccharomyces cerevisiae. Mol Cell Bio. 1987;7(6):2087-2096.
  2. Saur B, Henderson N. Site-specific DNA recombination in mammalian cells by the Cre recombinase of bacteriophage P1. Proc Natl Acad Sci U S A. 1988;85(14):5166-5170.

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