M^K: an Apparently Silent Allele at the MN Locus

Abstract

IN the course of investigations on M^G positive blood samples with an anti-N serum, A.P.¹, which, when used undiluted at room temperature, agglutinates NN but not MN red cells, attention was directed to a blood donor, Mrs. E. W.-K., whose cells were being used as a control: Mrs. W. had previously been grouped as M− N+, and her genotype was therefore thought to be NN, but her cells, contrary to expectation, were not agglutinated by serum A.P., which suggested that her true genotype was heterozygous rather than homozygous. Strong support for this was obtained when it was found that the red cells of Mrs. W.'s daughter gave the reactions M+ N−, since these are usually interpreted as representing the genotype MM, which, if it were the daughter's true genotype, would exclude Mrs. W.'s maternity. Such an exclusion, however, is not supported by the other blood groups of mother and daughter (and of Mr. W.), and it is rendered highly improbable by the fact that the daughter's cells, when tested with suitable anti-M sera, give a ‘single dose’ of M.