Genotyping PCRs. WBCs or tail DNA PCR was used for routine genotyping. A Cre-positive (experimental) and Cre-negative (control) male (F8 F/y) and female (F8 F/F) are shown for each tissue-specific Cre model. (A) Duplex PCR of WBC DNA using a common forward primer, P1, in combination with 2 alternative reverse primers, P2 and P3. As depicted in Figure 1B-C, a 712-bp product is amplified from the F8^F allele and a 462,bp product from the F8^KO allele. (B) Singleplex PCR of WBC DNA using primers P1 and P2 amplifies only the 712-bp F8^F allele-specific product. (C) Singleplex PCR of WBC DNA using primers P1 and P3 amplifies a 462 bp F8^KO allele-specific product but can also amplify a 1683-bp product from the F8^F allele. (D) A Cre-recombinase coding sequence–specific PCR of WBC DNA identifies Cre⁺ mice. No signal is seen for the Vav1-Cre transgene because it contains a codon-optimized iCre sequence, which is not recognized by the native Cre primers we used. (E) Duplex PCR analysis of tail DNA using primers P1, P2, and P3 detects both F8^F and F8^KO alleles, especially important for Vav1- and Tek-Cre mice, in which WBC DNA undergoes complete F8^F→KO gene conversion.