Second, Third Locus and 4a/4b Antigen Associations in Negroids and Gaucasoids

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Abstract
In Caucasoids the third locus antigen Hu (FJH or T-2) shows a 91% association with W27 and W10. Less than 10% of the Hu positive cells had an unknown antigen at the second locus. In a Negroid population from Zambia studied with 1972 Workshop data W27 was absent and W10 present in low frequency. Hu in contrast was present with twice the frequency seen in Caucasoids. Eighty-six % of positive cells had an unknown antigen at the second locus. Data from the use of platelet complement fixing sera suggests that this unknown allele was Da(6), an antigen present in very low frequency in Caucasoids. Recombination between second and third locus alleles has been proposed as an explanation for these associations. Associations of HL-A12 and Hu with 4a, W5 with 4b in Caucasoids and vice versa in the Negroids was demonstrated, and the possibility that this finding may be an indication of recombination between a separate 4a/4b locus and the second and third loci was discussed.