Southern blots of representative B lymphoma tumors from FGFR3/iMyc TG mice. (a) Tumor DNA was digested with EcoRI, subjected to electrophoresis, blotted, and hybridized with a 1.2 kb JH probe. Size markers are to the left, arrows to right indicate the 6.4 kb normal germline locus, and the 5.5 kb locus containing the knocked-in c-myc gene. Rearranged fragments are indicated by an R. (b) Tumor DNA was digested with BamHI and EcoRI, subjected to electrophoresis, blotted, and hybridized with a 1 kB Ck probe. The normal germline locus is indicated by an arrow.