Figure 4.

Advice for coinheritance of Wnt1-Cre2 and other alleles from the male lineage.

Depicted are four breeding schemes involving a conditional allele of Your Favorite Gene (YFG), a floxed reporter, and a paternal allele of Wnt1-Cre2. The cross and genotype ratios of the offspring are listed, and reporter activity is depicted in E9.5 embryos. (A) When no floxed allele is inherited from the sire, results are as expected. (B) When a floxed allele of YFG is present with Wnt1-Cre2 in the sire, it will transmit as a recombined (Δ) allele. This can complicate interpretation of results if heterozygous animals exhibit phenotypes. (C) Similarly, a reporter present in the sire will be fully recombined and be expressed ubiquitously in the next generation. (D) Coinheritance of Cre and a null allele will not affect results. Of note, many genotyping assays for conditional and null alleles rely on floxed sequences and are not able to detect a recombined (Δ) allele. This can lead to mis-genotyping of embryos and breeders, so primers that detect wild type, flox, and Δ alleles should always be used.