Characterization of deletion endpoints inW⁵⁷/W⁵⁷ and Ph/+ DNA. (A) Blot hybridization using a 0.6 kb BamH1-PstI probe corresponding to sequences at −147 kb showed novel DNA fragments inW⁵⁷ DNA digested with the restriction enzymesEcoR1 and HindIII (see Fig 1C). (B) Blot hybridization using a 0.8 kb XbaI-Xhol probe corresponding to sequences at −34 identified the same EcoRl fragment as theBamHl-Pstl probe (see Fig1C). PFGE analysis of high molecular weight DNA from +/+ and Ph/+ mice digested with Not1. Sequential hybridization with probes 2 and 4 (see Fig 1) is shown. Identical fragments were detected in Ph DNA with both probes. Size markers are indicated.