Linkage and sequence homology of two human immunoglobulin gamma heavy chain constant region genes

We report the nucleotide sequence of a gene encoding a human immunoglobulin Cγ2} region. Comparison with the previously determined Cγ4} sequence reveals that these two genes share extensive (~95%) homology in the three CH domain exons and adjacent noncoding regions. In contrast, hinge exons have diverged to a much greater degree, implying that natural selection has favored the generation of diversity in these coding regions. We have used the noncoding nucleotide differences to estimate that approximately 6-7 million years have elapsed since the occurrence of the gene duplication or correction event which generated the two identical ancestral genes. In addition we show that the two Cγ genes are arranged in human chromosomal DNA in the configuration 5'-Cγ2}-17 kilobase pairs -Cγ4}-3'