Definition of the RFLP alleles in the human immunoglobulin IGHG gene locus

In order to define more precisely the polymorphism of the human immunoglobulin IGHG (C gamma) genes and, consequently, to understand the structure and evolution of this multigene family, we have investigated the Restriction Fragment Length Polymorphisms (RFLP) of the IGHG genes in 113 unrelated individuals and 18 families. Using the restriction enzymes Bam HI, Sac I and Eco RI, and hybridization to a IGHG probe and to a specific IGHG3 (C gamma 3) probe, we describe 47 different restriction fragments (RF) in the IGHG locus, allowing us to define at least 15 RFLP alleles for the different IGHG genes. Our data demonstrate that the restriction fragment length polymorphism is occasionally due to the presence or absence of a given restriction site as a consequence of a point mutation, such as the creation of an Eco RI site, at the codon 3 of exon 2 in one IGHG4 allele (IGHG4*D2). However, most of the RFLP we observed seem to result from the insertion or deletion of a few hundred base pairs as illustrated by the IGHG3 polymorphism.