Erythrocyte automosaicism in some persons of known genotype.

We have estimated the proportions of non-A and non-B erythrocytes in some members of four families in which both parents were blood group AB, including two B homozygotes. The exceptional cell frequencies were not discernibly correlated with age. The B homozygotes had fewer non-B exceptional cells than their AB parents or sibs, but too many to represent independent losses of the B alleles. These results are not in agreement with the simplest expectations based on the mutational hypothesis of automosaicism.