A previous study [Mole et al. (1971) Biochem. J. 124, 301-318] showed several differences in sequence between the variable (V) regions of rabbit immunoglobulin Aa1 and Aa3 heavy chains. The inheritance of one such difference has been followed in a family of 38 rabbits by a radioautographic peptide-‘map’ technique and is shown to segregate in a Mendelian fashion. This clearly demonstrates the presence of a genetic marker in the rabbit heavy-chain V region, although the finding that Aa2 and Aa3 heavy chains have identity of sequence in the region studied obscures the relationship of this genetic marker to the a locus.
