Further observations on Kell blood groups in families ascertained via a mongol propositus.

Genes located on the unpaired portion of the humanX chromosome can readily be recognized, but as far as the autosomes are concerned it is not known upon which autosome any human gene is located. The common variety of mongolism is characterized by 21-trisomy, and offers a possible approach to the localization ofhuman autosomal genes. The model on which this approach is based was first formulated by Bateman (1960) and later developed by Shaw and Gershowitz (1962), Penrose (1963), Kaplan et al. (1964), and Goodman (1965). The essential experimental finding would be a reduced incidence of a recessive phenotype or homozygous genotype in the 21 trisomics as compared with nontrisomics, which would indicate that the genes controlling the polymorphism involved were located on chromosome 21. Results testing the ABO blood group system were published by Shaw and Gershowitz (1962, 1963), Chown and Lewis (1963), Kaplan et al. (1964), and Goodman and Thomas (1966). From these results it seems very unlikely that the ABO locus is on autosome 21. Evans et al. (1966) analysed data collected in Liverpool, in Buffalo, New York, U.S.A., and from a London series in the paper of Lang-Brown, Lawler, and Penrose (1952/53). Data on nine blood group systems and salivary ABH secretion were analysed. The only significant association between blood group phenotype and mongolism was found in the case of Kell where a significant excess of Kell-positive mongols was found. This finding raised the possibility that the Kell locus might be on chromosome 21. Objections to concluding that the human Kell locus was on chromosome 21 were discussed. Among others it was pointed out that since a number ofpolymorphisms had been investigated the statisti-