Southern blot analysis of the BamHI digest of tail DNA isolated from factor IX-knockout and normal mice. Analyses were performed as described in the Materials and Methods. After BamHI digestion, DNA was electrophoresed in a 0.7% agarose gel and transferred to a Hybond-N membrane. Factor IX-knockout mice gave the expected 7-kb and wild-type mice the expected 14-kb fragment after hybridization to the ³²P-labeled probe PE449. Lanes 1, 2, and 4 show factor IX-knockout male mice; lane 3 shows a normal male mouse; and lane 5 shows a (female) hemophilia B carrier.