Complexities of the MN Locus

Summary Fifteen examples of rare alleles of M and N were found in serial tests on 3,895 blood donors. They include: (1) a third example of Mc, which differs from the two previously known ones in that it is inherited as a McS (instead of Mcs) gene complex; (2) an example each of two genes whose phenotypic expression consists of the antigens M, N and Sta (Stones), but which differ so markedly, particularly as to the ‘amount’ of N formed, that they have been given separate symbols, namely, Mz and Mr; (3) an example of N2, a gene defined as giving rise to N, in a form weaker than ‘normal’, but not to any M antigen. The antigens arising from each of these four genes were studied in detail, by means of parallel tests with large panels of M and N reagents on blood samples from persons found in the 3,895 series, selected members of their families, and unrelated carriers of Mc, Mr, and N2. Also included in these studies were cell samples heterozygous for Mg and Mk, and ‘special’ sera such as anti-Mg, anti-Mk, anti-M’, etc. Anti-M’ subdivides groups M and MN in much the same way as anti-M1 does; in one respect at least, however, it differs clearly from the latter, namely, in its reactions with NMc and NMz cells. The results of tests with anti-Mk on cells of all available MNSs genotypes suggest the possibility that Mk is a precursor substance of the MNSs system.