Figure 2. Generation of ES cells with a conditional allele of Brca2.

To generate a conditional allele of Brca2 and to select the recombinants, two loxP sites were targeted upstream and downstream of the gene along with the 3ór 5´ halves of the human HPRT1 minigene and a Puromycin resistance gene by homologous recombination. To disrupt the other allele of Brca2, a Blasticidin resistance gene was targeted to exon 11. The conditional allele of Brca2 can be deleted by transiently expressing Cre. ES cells become HAT^r and Puro^s. However, such cells do not survive because of loss of functional BRCA2.