The inheritance of the blood group gene M k and some considerations on its possible nature.

. Although the gene Mk gives rise to none of the antigens of the MN or Ss series, its presence is revealed in the heterozygous state by the results of dosage experiments and by certain reactions related to some abnormality of the red cell surface. The corresponding character Mk may therefore be considered as dominant, and in matings of the type Mk x non-Mk, half of the children should consequently inherit the gene, and the other half not. Seventeen matings of the type mentioned, and 5 more presumed to be of this type, were analyzed in this respect: the results correspond closely with expectation. Work on so-called anti-Mk sera is reviewed and the results are discussed in conjunction with considerations on the possible nature of the gene Mk. The conclusion is reached that these sera do not contain a true blood group antibody and that Mk is either an amorph or a ‘built-in’ inhibitor gene at the MNSs locus.