Molecular cytogenetic study of species-specific chromosomal regions

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Since the draft sequences of the human genome were disclosed and publicized, this research field encounters a new phase. Gene function and biological significance of the constitution of human genome may be the main theme for further investigation. In the present study, search for the species-specific chromosomal regions has been attempted. In the present study, interests were focused on the evolutionary fusion point of human chromosome 2.It has been known that human chromosome 2 originated from the fusion of two ancestral primate chromosomes. This has been confirmed by chromosome banding and fluorescence in situ hybridization (FISH) with human chromosome-2-specific DNA libraries. In this study, the order of 38 cosmid clones derived from the human chromosome region 2q12-q14 was exactly determined by high-resolution FISH in human chromosome 2 and its homologous chromosomes in chimpanzees (Pan trogrodyzdes, 2n=48) and cynomolgus monkeys (Macaca fascicularis, 2n=42). This region includes the telomere-to-telomere fusion point of two ancestral ape-type chromosomes. As a result of comparisons with chimpanzee and cynomolgus monkey chromosomes, human chromosome region 2q12-q14 was found to correspond to the short arms of chimpanzee chromosomes 12 and 13 and cynomolgus monkey chromosomes 9 and 15. It is noted that no difference was detected in the relative order of the cosmid clones between human and chimpanzee chromosomes. This suggests that two ancestral ape-type chromosomes fused tandemly at telomeres to form human chromosome 2, and the genomic organization of this region is thought to be considerably conserved. In the cynomolgus monkey, however, the order of clones in each homologue was inverted. Interestingly, the number of repeated arrays around the fusion point was found to exhibit polymorphism.