Gene conversion in human immunoglobulin γ locus shown by unusual location of IgG allotypes

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Abstract
The constant region of the γ1, γ2 and γ3 heavy chains of the human IgGl, IgG2 and IgG3 immunoglobulins carries antigenic determinants or G1m, G2m and G3m allotypes, which are genetic markers of these subclasses. The exceptional presence on γl and γ2 chains of Gm allotypes usually located on the CH3 domain of γ3 shows an unexpected clustering of base changes and subsequent identity of short DNA sequences in the CH3 exon of the non‐allelic γ1,γ2 and γ3 genes. Such clusters of substitutions are not easily explained on the classical basis of point mutations. A gene conversion, which substituted a segment of the γ1 or γ2 gene with the homologous region of the non‐allelic γ3 gene, is more likely. Other examples of possible conversion involving the γ genes are described. The conservation or the restoration of short sequences produced by the conversion events might be related to the biological properties of the constant region of the heavy chains.