Hominoid genes meet on middle ground

November 14, 1999

Evolution loves a fluid genome. Chromosomes that copy, shift, and mutate their genes provide the fuel for evolutionary change. Indeed, as shown by Evan Eichler (Case Western Reserve School of Medicine) and colleagues in the November issue of Genome Research, the hominoid genome has used diverse strategies for self-alteration, including a newly discovered form of gene copying called pericentromeric duplication.

Scientists have discovered numerous examples of gene duplication in the history of our genome. In some cases, mismatching exchanges between chromosomes have strung multiple copies of a gene together, like beads on a necklace. In rarer, ancient episodes, the genome acquired extra copies of whole chromosomes. However, data from the Human Genome Project reveals a potentially different form of gene duplication occurring at the centers of chromosomes, near the centromeres. Researchers sequencing these pericentromeric regions have unearthed copies of genes whose original versions reside in distant regions of the genome.

Now Eichler and colleagues propose a novel mechanism for these duplication events, involving a unique, repeated DNA element (CAGGG) discovered in the pericentromeric region. Using fluorescent probes, they imaged the locations of the CAGGG repeats on human chromosomes and found multiple copies distributed exclusively near centromeres. Furthermore, the repeats they examined in detail were flanked with copies of disparately located genes. By comparing these copies with the original genes, the researchers estimated the genes duplicated only 10 to 25 million years ago, well after the evolutionary divergence of hominoids from Old World primates. Indeed, Old World primates, such as the baboon, possess far fewer CAGGG repeats than hominoids, such as the human, indicating the repeats themselves multiplied after the divergence. Altogether, these data suggest that CAGGG repeats mediate a recently active form of gene copying, which has pulled a disparate collection of genes to the central regions of hominoid chromosomes and thus created a potential breeding ground for new human genes.
-end-
Contact (author):

Evan Eichler
Center for Human Genetics
Case Western Reserve School of Medicine
Cleveland, Ohio 44106
Email: eee@po.cwru.edu
Fax: 216-368-3432

Cold Spring Harbor Laboratory

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