THE G4 GENE IS DUPLICATED IN 44-PERCENT OF HUMAN-IMMUNOGLOBULIN HEAVY-CHAIN CONSTANT-REGION HAPLOTYPES

The structure of the human immunoglobulin heavy chain constant region (IGHC), on chromosome 14q32, comprises nine CH genes and two pseudogen es, all originating from multiple duplication events. Continuing evolu tion of the region is demonstrated by the finding of various types of duplicated and deleted haplotypes, which together add up to 6%. Here w e provide molecular and genetic evidence that the G4 gene is duplicate d in 44% of IGHC haplotypes in the Italian population. The duplication spans about 20 kb of genomic DNA and probably originated through uneq ual crossing over. Refined characterisation of the genomic region down stream from the G4 gene improves our knowledge of the evolutionary his tory of CH genes.