Conversely, the loss of the wild‐type Pax5 allele in B220low B cells and B‐ALL cells was confirmed by quantitative PCR analyses with primers amplifying a 150‐bp sequence in Pax5 intron 3 that was absent on the Pax5Jak2 allele (Appendix Fig S3A). Here, PAX5 is linked to acute lymphoblastic leukemia.