FIG. 1.
Homologous recombination in DT40 cells on a modified human chromosome 11 with the human β-globin locus. The genes of the β-globin locus and the upstream HSs are indicated, as well as the modification introduced into the locus in an earlier study (13) (see the text). Homologous recombination creates the 5-neo-4 mutation. After transfer of this chromosome into MEL cells, transient expression of the respective site-specific recombinases creates the indicated mutations. Abbreviations: neo, neomycin resistance gene; hygro, hygromycin B resistance gene; tk, thymidine kinase gene for negative selection. FLP recombinase recognition sites are depicted as open triangles; Cre recombinase recognition sites are depicted as solid triangles.