DNA ANALYSIS OF THE IMMUNOGLOBULIN IGHG LOCI IN A MANDENKA POPULATIONFROM EASTERN SENEGAL - CORRELATION WITH GM HAPLOTYPES AND HYPOTHESES FOR THE EVOLUTION OF THE IG CH REGION

This study presents restriction fragment length polymorphism (RFLP) an d serological analyses of the immunoglobulin CH loci in a sample of 10 0 individuals from a Senegalese Mandenka population. The RFLP variabil ity is mostly the result of large DNA insertions or deletions in the n on-coding flanking regions of the IGHG genes, and to variable number o f tandem repeat-like patterns within their 5'-switch sequences. Howeve r, part of the IGHG3 polymorphism also corresponds to a variable numbe r of exons coding for the flexible hinge segment of the IgG3 antibody (the 4-exon and 3-exon forms, and a newly described 2-exon form). This diversity presents relevant associations with Gm haplotypes, suggesti ng that molecular rearrangements of the G3 hinge are related to the ev olution of the Gm polymorphism. Non-significant correlation coefficien ts are found between Gm haplotypes and A(2)m alleles in the Mandenka, indicating that these loci may have reached equilibrium through recomb ination. The effect of recombination on linkage disequilibrium is more generally revealed, across the Ig CH genomic region, by a significant decrease of D' values with increasing physical distances between the loci on the chromosome.