The organization of the human immunoglobulin CH gene suggests that a gene duplication involving the Cγ-Cγ-C∈-Cα region has occurred during evolution. We previously showed that both chimpanzee and gorilla have two 5′-C∈-Cα-3′, as in human, and that orangutan, gibbon, and Old World monkeys have one C∈ gene and one, two, and one Cα gene(s), respectively. In addition to these clustered CH genes, there is one processed C∈ pseudogene in each species. The present study revealed that orangutan and crab-eating macaque (an Old World monkey) both have one 5′-C∈-Cα-3′ and that gibbon has two 5′-C∈-Cα-3′, one C∈ gene of which is completely deleted. By Southern analysis, the number of Cγ genes in all the non-human hominoids was estimated to be four to five, as in human, in comparison with two for crab-eating macaque. The Cμ and Cδ genes were estimated to be present as single copies in both hominoids and crab-eating macaque. Furthermore, it was proved that there are two copies of the C∈ 5′-flanking region in both the orangutan and the gibbon genomes. These results show that gene duplication including the Cγ-Cγ-C∈-Cα genes occurred in the common ancestor of hominoids and that subsequent deletion of the C∈ gene (in orangutan, including one of the Cα genes) occurred independently in each hominoid species. © 1992.
