No Distinction of Orthology/Paralogy between Human and Chimpanzee Rh Blood Group Genes

Abstract

On human (Homo sapiens) chromosome 1, there is a tandem duplication encompassing Rh blood group genes (Hosa_RHD and Hosa_RHCE). This duplication occurred in the common ancestor of humans, chimpanzees (Pan troglodytes), and gorillas, after splitting from their common ancestor with orangutans. Although several studies have been conducted on ape Rh blood group genes, the clear genome structures of the gene clusters remain unknown. Here, we determined the genome structure of the gene cluster of chimpanzee Rh genes by sequencing five BAC (Bacterial Artificial Chromosome) clones derived from chimpanzees. We characterized three complete loci (Patr_RH alpha, Patr_RH beta, and Patr_RH gamma). In the Patr_RH beta locus, a short version of the gene, which lacked the middle part containing exons 4-8, was observed. The Patr_RH alpha and Patr_RH beta genes were located on the locations corresponding to Hosa_RHD and Hosa_RHCE, respectively, and Patr_RH gamma was in the immediate vicinity of Patr_RH beta. Sequence comparisons revealed high sequence similarity between Patr_RH beta and Hosa_RHCE, while the chimpanzee Rh gene closest to Hosa_RHD was not Patr_RH alpha but rather Patr_RH gamma. The results suggest that rearrangements and gene conversions frequently occurred between these genes and that the classic orthology/paralogy dichotomy no longer holds between human and chimpanzee Rh blood group genes.