Southern analysis of the ES cell clones. (A) The ES cell clone (D11) and 129/Sv mouse DNA were digested with Xba I and hybridized with probe A. The wild-type clone (+/0) showed an 8.0-kb fragment, the recombinant disrupted clone (−/0) showed a 6.4-kb band. (B) The same DNA samples were digested with XbaI and hybridized with probe B. The wild-type clone (+/0) showed a 3.9-kb band, while the mutant allele (−/0) showed a 4.6-kb band.