The adult β-globin genes of the “single” type mouse C57BL

A set of four clones containing the two adult β-globin genes of the “single” type mouse C57BL/10 (genotype Hbb^s/Hbb^s) were isolated from a library of cloned restriction fragments. The two genes, designated βs and βt, were physically mapped onto a 32 kb segment of the chromosome carried by the four clones. βs and βt form a stable heteroduplex 1850 bp long, indicating that they are intact and conserved at this level of resolution throughout their length, including their intervening sequences. The βs gene is allelic with the βdmaj gene of the BALB/ c mouse (genotype Hbb^d/Hbb^d). These two alleles, as well as their surrounding sequences, are highly conserved. In contrast, heteroduplexes of βt with its BALB/c allele, βdmin, revealed three extensive but localized rearrangements. One region of non-homology falls within the large intervening sequence, IVS2. To the 5′ side of the βt/βdmin gene position two unequal substitutions were observed; each results in the net insertion of about 1000 bp into the Hbb^d chromosome. The β/βdmin gene position is bracketed by a 1450 bp inverted repeat. One of the 1000 bp substitutions maps within this inverted repeat.