Tentative evidence for 3--4 haematopoetic stem cells in man.

Blood specimens from a random sample of 981 South African Negroid females were typed electrophoretically inter alia for their G-6-PD phenotypes, The allele frequency for GdB and GdnonB was found to be 0.8126 and 0.1874 respectively. Calculating the number of individuals expected for each phenotypic class, a highly significant deviation from the Hardy-Weinberg equilibrium became manifest, i.e. there was a deficit of 24.6% of heterozygotes and an excess of 12.3% of each of the two classes of homozygotes. Several possible reasons for this discrepancy e.g. the effects of pooling sub-samples, selection and misclassifications due to insufficient staining were examined and were found not be likely explanations for the observed phenomenon. Instead, the result is interpreted as due to only 3--4 stem cells which give rise to the haematopoetic system in man.