CA mice were generated by replacing the adult mouse β globin genes with a human γ^HPFHδβ⁰ globin gene cassette in mouse ES cells. (A) Scheme of targeted gene replacement of the adult mouse β globin genes by a human γ^HPFHδβ⁰ globin gene cassette in mouse ES cells. The hyg marker gene was deleted by breeding to CRE recombinase transgenic mice.²⁰  (B) Southern blot confirmation of correct homologous recombination. The 5′ probe hybridizes with a 9.2-kb XbaI fragment from the wild-type allele and a 7.9-kb fragment from the human globin KI allele. The 3′ probe derived from part of the β^min globin gene anneals to a 14.8-kb EcoRI fragment from the β^min globin gene, a 7.3-kb fragment from the β^maj globin gene, and a 10.3-kb fragment from the human globin KI allele.