Abstract
The Hbbd allele at the hemoglobin beta chain locus of Mus musculus is composed of two linked genes, coding for structurally different beta chains, βdmin and βdmaj. Mus caroli has only one beta chain, which combines structural features of both βdmin and βdmaj and thus may be a Lepore type of beta chain. Sequence data suggest that selection may have been important in the evolution of the mouse beta chains.