Accession numbers for the genes and gene products discussed in this paper are βH1 globin (GenBank NM_008219), βmaj globin (J00413) (in situ), βmaj/min globin (NM_008220) (real time PCR), ɛy globin cDNA (NM_008221) from the Fantom (Functional Annotation of Mouse) database (http://fantom2.gsc.riken.jp), ζ globin (GenBank NM_010405), and mouse Sox6 (U32614).