Targeted disruption of the ζ- and α1-globin genes. Top: Map of the mouse α-globin locus with its three genes: ζ, α1, and α2. Middle: Maps of targeting vectors containing 6 Kb and 7.5 Kb genomic sequences of the ζ- and α1-genes, respectively. In both cases, interruption by homologous recombination would result in the insertion of the PGK-Neo cassette21 close to the middle of the respective genomic fragments. Note that in both cases the inserted PGK-Neo cassette would be transcribed in the direction opposite that of the ζ- and α-genes. Homologous recombination would introduce the PGK-Neo cassette at the Xba I site at the end of exon-1 of the ζ-gene, and would replace a 295 bp BamHI fragment containing a portion of the first intron and the second exon of the α1-gene. Bottom: Shown are examples of restriction endonuclease analyses of tail DNA prepared from wild-type (+/+), heterozygous (+/−), and homozygous (−/−) ζ- and α1-mutant mice. The position of the wild-type and mutant DNA fragments detected by the probe are indicated by labeled arrows. Filters were probed with the indicated genomic fragments (5′ ζ KO probe and 3′ α KO probe) both of which reside outside the region involved in homologous recombination. For the ζ-mutation, DNA was digested with EcoRV and probed with a 1.8 Kb R5-Xba I fragment. For the α1 mutation, DNA was digested with EcoRI and probed with 1.2 Kb BamHI-EcoRI fragment. Restriction endonuclease symbols: R5 = EcoRV; X = Xba I; E = EcoRI; B = BamHI.