Serogenetic studies on the inhabitants of Tristan da Cunha.

The inhabitants of Tristan da Cunha, a remote island in the South Atlantic, number about 300 and are direct descendants of a small number of individuals who settled there in the first half of the nineteenth century. Some serogenetic studies were carried out on the islanders when they were evacuated to England in 1961 but 160 individuals have now been tested for a much wider range of gene markers. No variation was found at 15 loci while considerable variation was encountered at 12 loci. In particular, the high frequency of A1 and the complete absence of A2 in the ABO system was confirmed; the high frequency of Ro (cDe) in the Rhesus system and GdA, an allele at the G6PD locus, as well as the presence of three haplotypes in the Gm system (Gm1,5,6,14,17, Gm1,5,6,17 and Gm1,5,13,14,17) confirm the known historical origin of the women founders who came from St Helena. Although the degree of inbreeding is high there is no significant deficiency of heterozygotes in the eight informative systems.