The β-globin loci in mouse and human. The β-globin loci consist of the LCR, the globin genes and insulator elements HS5 and 3′HS1. In the mouse locus, the ɛy and βH1 are transcribed the in embryo, while the βmaj and βmin are transcribed in the adult. In the human locus, the globin genes are transcribed in three developmental stages; ɛ in the embryo, Gγ and Aγ in the fetus, and δ and β in adult.