The PR/SET domain 1 (PRDM1 or BLIMP1) gene encodes a transcriptional repressor. It inhibits the expression of the interferon-β (IFN-β) gene and plays a critical role in mouse germ cell formation. PRDM1 is widely expressed during development, including in migrating germ cells. Prdm1-iCre (Blimp1-iCre) mice are generated by integrating the P2A-iCre expression element at the stop codon of the mouse Prdm1 gene. When Prdm1-iCre (Blimp1-iCre) mice are crossed with mice containing loxP sites, Cre recombinase-mediated sequence recombination occurs in the offspring’s primordial germ cells.